Add Prefect Horizon account commands (#4786)

* feat: add Horizon account commands

* feat: add a Horizon host option to login

* feat: refine Horizon account output

* style: refine Horizon output headings

* feat: describe device authorization requests

* fix: preserve Horizon command contracts

* fix: preserve environment credentials on logout

* fix: keep Horizon state reads consistent

* docs: hide the Horizon host override

docs/cli/overview.mdx

@@ -28,6 +28,9 @@ fastmcp --help
 | [`generate-cli`](/cli/generate-cli) | Scaffold a standalone typed CLI from a server's tool schemas |
 | [`project prepare`](/cli/running#pre-building-environments) | Pre-install dependencies into a reusable uv project |
 | [`auth cimd`](/cli/auth) | Create and validate CIMD documents for OAuth |
+| `login` | Sign in to Prefect Horizon with a browser device flow |
+| `whoami` | Show the current Horizon account |
+| `logout` | Revoke the current Horizon key and remove the local credential |
 | `version` | Print version info (`--copy` to copy to clipboard) |
 
 ## Server Targets
@@ -81,6 +84,38 @@ Run [`fastmcp discover`](/cli/client#discovering-configured-servers) to see what
 
 ## Authentication
 
+### Prefect Horizon Account
+
+Use the top-level account commands to manage the credential for Prefect Horizon.
+
+```bash
+fastmcp login
+fastmcp whoami
+fastmcp logout
+```
+
+`fastmcp login` first uses `HORIZON_API_KEY` or a valid stored key when one is available.
+When login needs a new key, it shows a verification URL and code.
+It opens a browser when the terminal supports it.
+If the browser does not open, use the shown URL and code on another device.
+To switch accounts, run `fastmcp logout` before you run `fastmcp login` again.
+
+Login stores only the personal Horizon API key.
+It does not select or store a deployment organization.
+`fastmcp whoami` gets the current user from Horizon.
+`fastmcp logout` attempts to revoke the stored key and always removes its local credential.
+
+Set `HORIZON_API_KEY` to use an environment credential instead.
+The CLI gives that value first precedence and never stores it.
+When this variable controls the session, logout does not revoke or remove any credential.
+Remove the variable from your environment to sign out.
+
+Use `--json` for stable command results.
+During JSON login, the verification challenge goes to stderr and the final result goes to stdout.
+JSON mode does not open a browser or ask a question.
+
+### MCP Server Authentication
+
 When targeting an HTTP URL, the CLI enables OAuth authentication by default. If the server requires it, you'll be guided through the flow (typically opening a browser). If it doesn't, the setup is a silent no-op.
 
 To skip authentication entirely — useful for local development servers — pass `--auth none`:

docs/deployment/prefect-horizon.mdx

@@ -13,6 +13,39 @@ Horizon includes a **free personal tier for FastMCP users**, making it the faste
 Horizon is free for personal projects. Enterprise governance features are available for teams deploying to thousands of users.
 </Info>
 
+## FastMCP CLI Account
+
+Sign in to Horizon from the FastMCP CLI with the device authorization flow.
+
+```bash
+fastmcp login
+```
+
+The command uses an environment key or a valid stored key when one is available.
+When login needs a new key, it shows a verification URL and code before it opens the browser.
+If the browser cannot open, visit the shown URL and enter the code.
+To switch accounts, run `fastmcp logout` before you run `fastmcp login` again.
+New users can register and create their first Horizon organization in the browser.
+
+Check the active account after login.
+
+```bash
+fastmcp whoami
+```
+
+Remove the local credential and revoke the active personal API key when possible.
+
+```bash
+fastmcp logout
+```
+
+Login does not select or store a deployment organization.
+
+For an agent or a CI process, set `HORIZON_API_KEY` instead of storing a key.
+The CLI never writes the environment value to its credential file.
+When this variable controls the session, logout does not revoke or remove any credential.
+Remove the variable from the environment to sign out.
+
 ## The Platform
 
 Horizon is organized into four integrated pillars:

fastmcp_slim/fastmcp/cli/cli.py

@@ -21,6 +21,7 @@ import fastmcp
 from fastmcp.cli import run as run_module
 from fastmcp.cli.auth import auth_app
 from fastmcp.cli.client import call_command, discover_command, list_command
+from fastmcp.cli.deploy.command import login, logout, whoami
 from fastmcp.cli.generate import generate_cli_command
 from fastmcp.cli.install import install_app
 from fastmcp.utilities.cli import is_already_in_uv_subprocess, load_and_merge_config
@@ -1134,6 +1135,11 @@ app.command(generate_cli_command, name="generate-cli")
 # Add auth subcommand group (includes CIMD commands)
 app.command(auth_app)
 
+# Add Prefect Horizon account commands
+app.command(login)
+app.command(logout)
+app.command(whoami)
+
 
 if __name__ == "__main__":
     app()

fastmcp_slim/fastmcp/cli/deploy/command.py

@@ -0,0 +1,398 @@
+"""Public Prefect Horizon authentication commands."""
+
+from __future__ import annotations
+
+import os
+import platform
+import sys
+import webbrowser
+from typing import Annotated, NoReturn
+
+from cyclopts import Parameter
+from pydantic import SecretStr
+from rich.status import Status
+
+import fastmcp
+from fastmcp.cli.deploy.authentication import (
+    DeviceAuthorizationDeniedError,
+    DeviceAuthorizationError,
+    DeviceAuthorizationExpiredError,
+    authorize_device,
+)
+from fastmcp.cli.deploy.configuration import (
+    ConfigurationStore,
+    HorizonConfiguration,
+)
+from fastmcp.cli.deploy.credentials import (
+    AuthenticationRequiredError,
+    CredentialStore,
+    ResolvedCredential,
+)
+from fastmcp.cli.deploy.horizon_client import (
+    DeviceAuthorization,
+    DeviceMetadata,
+    HorizonClient,
+    HorizonResponseError,
+    HorizonUnauthorizedError,
+    HorizonUnavailableError,
+    HorizonUser,
+)
+from fastmcp.cli.deploy.output import (
+    CommandName,
+    ErrorCategory,
+    emit_device_challenge,
+    emit_environment_logout,
+    emit_error,
+    emit_identity,
+    emit_logout,
+    start_device_approval_status,
+    stop_device_approval_status,
+)
+from fastmcp.cli.deploy.state import StateFileError, state_lock
+
+JsonOption = Annotated[
+    bool,
+    Parameter(
+        name="--json",
+        help="Write one final JSON result to stdout",
+        negative=(),
+    ),
+]
+HostOption = Annotated[
+    str | None,
+    Parameter(
+        name="--host",
+        help="Use and save a different Horizon host URL",
+    ),
+]
+
+
+def _can_open_browser() -> bool:
+    return sys.stdin.isatty() and sys.stdout.isatty()
+
+
+def _device_metadata() -> DeviceMetadata:
+    return DeviceMetadata(
+        device_name=platform.node() or None,
+        platform=platform.system().lower() or None,
+        architecture=platform.machine().lower() or None,
+        client_version=fastmcp.__version__,
+    )
+
+
+def _load_session_snapshot(
+    credentials: CredentialStore,
+) -> tuple[HorizonConfiguration, ResolvedCredential | None]:
+    with state_lock(credentials.path.parent):
+        configuration = ConfigurationStore(credentials.path.parent).load()
+        environment_key = os.environ.get("HORIZON_API_KEY")
+        if environment_key:
+            credential = ResolvedCredential(
+                api_key=SecretStr(environment_key),
+                source="environment",
+            )
+        else:
+            stored_key = credentials.load()
+            credential = (
+                ResolvedCredential(api_key=stored_key, source="stored")
+                if stored_key is not None
+                else None
+            )
+    return configuration, credential
+
+
+def _fail(
+    command: CommandName,
+    category: ErrorCategory,
+    message: str,
+    *,
+    json_output: bool,
+    details: dict[str, object] | None = None,
+) -> NoReturn:
+    emit_error(
+        command,
+        category,
+        message,
+        json_output=json_output,
+        details=details,
+    )
+    raise SystemExit(1)
+
+
+def _fail_for_expected_error(
+    command: CommandName,
+    error: Exception,
+    *,
+    json_output: bool,
+) -> NoReturn:
+    if isinstance(error, AuthenticationRequiredError):
+        _fail(
+            command,
+            "authentication_required",
+            "Run `fastmcp login` to sign in to Prefect Horizon.",
+            json_output=json_output,
+        )
+    if isinstance(error, HorizonUnauthorizedError):
+        _fail(
+            command,
+            "authentication_invalid",
+            "The Horizon credential is not valid. Run `fastmcp login` again.",
+            json_output=json_output,
+        )
+    if isinstance(error, DeviceAuthorizationDeniedError):
+        _fail(
+            command,
+            "authorization_denied",
+            "The device authorization request was denied.",
+            json_output=json_output,
+        )
+    if isinstance(error, DeviceAuthorizationExpiredError):
+        _fail(
+            command,
+            "authorization_expired",
+            "The device authorization request expired. Run the command again.",
+            json_output=json_output,
+        )
+    if isinstance(error, DeviceAuthorizationError):
+        _fail(
+            command,
+            "authorization_failed",
+            "The device authorization request failed. Run the command again.",
+            json_output=json_output,
+        )
+    if isinstance(error, HorizonUnavailableError):
+        _fail(
+            command,
+            "horizon_unavailable",
+            "The Horizon API is unavailable. Try again later.",
+            json_output=json_output,
+        )
+    if isinstance(error, HorizonResponseError):
+        _fail(
+            command,
+            "horizon_error",
+            "Horizon returned an unexpected response. Try again later.",
+            json_output=json_output,
+        )
+    if isinstance(error, StateFileError):
+        _fail(
+            command,
+            "state_error",
+            "The local Horizon state is invalid.",
+            json_output=json_output,
+        )
+    raise error
+
+
+async def _get_user(
+    api_origin: str,
+    credential: ResolvedCredential,
+) -> HorizonUser:
+    async with HorizonClient(api_origin, api_key=credential.api_key) as client:
+        return await client.get_current_user()
+
+
+async def login(
+    *,
+    host: HostOption = None,
+    json_output: JsonOption = False,
+) -> None:
+    """Sign in to Prefect Horizon."""
+    credentials = CredentialStore()
+
+    try:
+        configuration_store = ConfigurationStore()
+        requested_configuration: HorizonConfiguration | None = None
+        if host is not None:
+            try:
+                requested_configuration = configuration_store.set_api_origin(
+                    host,
+                    credentials=credentials,
+                )
+            except ValueError:
+                _fail(
+                    "login",
+                    "invalid_host",
+                    "The Horizon host must be an HTTP origin.",
+                    json_output=json_output,
+                )
+
+        configuration, credential = _load_session_snapshot(credentials)
+        if (
+            requested_configuration is not None
+            and configuration.api_origin != requested_configuration.api_origin
+        ):
+            raise StateFileError("The Horizon host changed during login")
+
+        async def device_authorization():
+            approval_status: Status | None = None
+
+            def show_challenge(challenge: DeviceAuthorization) -> None:
+                nonlocal approval_status
+                emit_device_challenge(challenge, json_output=json_output)
+                approval_status = start_device_approval_status(json_output=json_output)
+
+            try:
+                async with HorizonClient(configuration.api_origin) as client:
+                    return await authorize_device(
+                        client,
+                        metadata=_device_metadata(),
+                        on_challenge=show_challenge,
+                        open_browser=not json_output and _can_open_browser(),
+                        browser_opener=webbrowser.open,
+                    )
+            finally:
+                stop_device_approval_status(approval_status)
+
+        async def interactive_credential() -> ResolvedCredential:
+            api_key = await device_authorization()
+            credentials.save_for_origin(
+                api_key,
+                expected_api_origin=configuration.api_origin,
+            )
+            return ResolvedCredential(api_key=api_key, source="interactive")
+
+        if credential is None:
+            credential = await interactive_credential()
+
+        try:
+            user = await _get_user(
+                configuration.api_origin,
+                credential,
+            )
+        except HorizonUnauthorizedError:
+            if credential.source == "environment":
+                raise
+
+            credentials.clear_if_matches(
+                credential.api_key,
+                expected_api_origin=configuration.api_origin,
+            )
+            if credential.source == "interactive":
+                raise
+
+            credential = await interactive_credential()
+            try:
+                user = await _get_user(
+                    configuration.api_origin,
+                    credential,
+                )
+            except HorizonUnauthorizedError:
+                credentials.clear_if_matches(
+                    credential.api_key,
+                    expected_api_origin=configuration.api_origin,
+                )
+                raise
+    except (
+        AuthenticationRequiredError,
+        DeviceAuthorizationError,
+        HorizonResponseError,
+        HorizonUnauthorizedError,
+        HorizonUnavailableError,
+        StateFileError,
+    ) as error:
+        _fail_for_expected_error("login", error, json_output=json_output)
+
+    emit_identity(
+        "login",
+        user,
+        json_output=json_output,
+    )
+
+
+async def whoami(
+    *,
+    json_output: JsonOption = False,
+) -> None:
+    """Show the current Prefect Horizon user."""
+    credentials = CredentialStore()
+    configuration: HorizonConfiguration | None = None
+    credential: ResolvedCredential | None = None
+
+    try:
+        configuration, credential = _load_session_snapshot(credentials)
+        if credential is None:
+            raise AuthenticationRequiredError("Horizon authentication is required")
+        user = await _get_user(
+            configuration.api_origin,
+            credential,
+        )
+    except HorizonUnauthorizedError as error:
+        if (
+            configuration is not None
+            and credential is not None
+            and credential.source == "stored"
+        ):
+            try:
+                credentials.clear_if_matches(
+                    credential.api_key,
+                    expected_api_origin=configuration.api_origin,
+                )
+            except StateFileError as cleanup_error:
+                _fail_for_expected_error(
+                    "whoami",
+                    cleanup_error,
+                    json_output=json_output,
+                )
+        _fail_for_expected_error("whoami", error, json_output=json_output)
+    except (
+        AuthenticationRequiredError,
+        HorizonResponseError,
+        HorizonUnavailableError,
+        StateFileError,
+    ) as error:
+        _fail_for_expected_error("whoami", error, json_output=json_output)
+
+    emit_identity(
+        "whoami",
+        user,
+        json_output=json_output,
+    )
+
+
+async def logout(
+    *,
+    json_output: JsonOption = False,
+) -> None:
+    """Revoke the current Horizon key and remove the local credential."""
+    credentials = CredentialStore()
+
+    if os.environ.get("HORIZON_API_KEY"):
+        emit_environment_logout(json_output=json_output)
+        return
+
+    try:
+        configuration, credential = _load_session_snapshot(credentials)
+        if credential is None:
+            emit_logout(remote_revoked=False, json_output=json_output)
+            return
+
+        async with HorizonClient(
+            configuration.api_origin,
+            api_key=credential.api_key,
+        ) as client:
+            try:
+                await client.revoke_current_api_key()
+            finally:
+                credentials.clear_if_matches(
+                    credential.api_key,
+                    expected_api_origin=configuration.api_origin,
+                )
+    except HorizonUnauthorizedError:
+        emit_logout(remote_revoked=False, json_output=json_output)
+        return
+    except (HorizonResponseError, HorizonUnavailableError):
+        _fail(
+            "logout",
+            "remote_revocation_failed",
+            "The local credential was removed, but the remote key can remain active.",
+            json_output=json_output,
+            details={
+                "localCredentialRemoved": True,
+                "remoteCredentialMayRemain": True,
+            },
+        )
+    except StateFileError as error:
+        _fail_for_expected_error("logout", error, json_output=json_output)
+
+    emit_logout(remote_revoked=True, json_output=json_output)

fastmcp_slim/fastmcp/cli/deploy/credentials.py

@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 import os
+import secrets
 from collections.abc import Awaitable, Callable, Mapping
 from dataclasses import dataclass
 from pathlib import Path
@@ -96,6 +97,32 @@ class CredentialStore:
                 raise StateFileError("The Horizon host changed during login")
             self.save(api_key)
 
+    def clear_if_matches(
+        self,
+        api_key: SecretStr | str,
+        *,
+        expected_api_origin: str,
+    ) -> None:
+        """Clear a key only while its Horizon origin and value are active."""
+        from fastmcp.cli.deploy.configuration import ConfigurationStore
+
+        expected_api_origin = normalize_api_origin(expected_api_origin)
+        expected_api_key = (
+            api_key.get_secret_value() if isinstance(api_key, SecretStr) else api_key
+        )
+        with state_lock(self.path.parent):
+            active_api_origin = ConfigurationStore(self.path.parent).load().api_origin
+            active_api_key = self.load()
+            if (
+                active_api_origin == expected_api_origin
+                and active_api_key is not None
+                and secrets.compare_digest(
+                    active_api_key.get_secret_value(),
+                    expected_api_key,
+                )
+            ):
+                self.clear()
+
     def clear(self) -> None:
         remove_state(self.path)
 

fastmcp_slim/fastmcp/cli/deploy/output.py

@@ -0,0 +1,297 @@
+"""Stable terminal and JSON output for Horizon CLI commands."""
+
+from __future__ import annotations
+
+import json
+import sys
+from typing import Literal
+
+from rich import box
+from rich.align import Align
+from rich.console import Console, Group
+from rich.padding import Padding
+from rich.panel import Panel
+from rich.status import Status
+from rich.table import Table
+from rich.text import Text
+
+from fastmcp.cli.deploy.horizon_client import DeviceAuthorization, HorizonUser
+
+CommandName = Literal["login", "logout", "whoami"]
+ErrorCategory = Literal[
+    "authentication_invalid",
+    "authentication_required",
+    "authorization_denied",
+    "authorization_expired",
+    "authorization_failed",
+    "horizon_error",
+    "horizon_unavailable",
+    "invalid_host",
+    "remote_revocation_failed",
+    "state_error",
+]
+
+console = Console()
+error_console = Console(stderr=True)
+
+
+def _write_json(payload: object, *, stderr: bool = False) -> None:
+    stream = sys.stderr if stderr else sys.stdout
+    print(json.dumps(payload, separators=(",", ":")), file=stream, flush=True)
+
+
+def _banner(title: str, *, style: str) -> Panel:
+    return Panel(
+        Align.center(Text(title, style=f"bold {style}")),
+        box=box.ROUNDED,
+        border_style=style,
+        padding=(0, 1),
+        width=52,
+    )
+
+
+def _account_panel(
+    user: HorizonUser,
+    *,
+    title: str,
+    message: str,
+) -> Panel:
+    name = Text(user.name or user.email, style="bold")
+    details: list[Text] = [name]
+    if user.name:
+        details.append(Text(user.email, style="cyan"))
+    details.extend([Text(), Text(message, style="green")])
+    return Panel(
+        Group(*details),
+        title=Text(title, style="bold green"),
+        title_align="left",
+        box=box.ROUNDED,
+        border_style="green",
+        padding=(1, 2),
+        width=52,
+    )
+
+
+def _format_duration(seconds: int) -> str:
+    if seconds % 60 == 0:
+        minutes = seconds // 60
+        unit = "minute" if minutes == 1 else "minutes"
+        return f"{minutes} {unit}"
+    unit = "second" if seconds == 1 else "seconds"
+    return f"{seconds} {unit}"
+
+
+def emit_device_challenge(
+    authorization: DeviceAuthorization,
+    *,
+    json_output: bool,
+) -> None:
+    """Show a device challenge before polling starts."""
+    if json_output:
+        _write_json(
+            {
+                "event": "device_authorization",
+                "verificationUrl": authorization.verification_uri,
+                "verificationUrlComplete": authorization.verification_uri_complete,
+                "userCode": authorization.user_code,
+            },
+            stderr=True,
+        )
+        return
+
+    console.print()
+    console.print(_banner("Deploy FastMCP on Horizon", style="magenta"))
+    console.print()
+    console.print(Text("✓ Device authorization started", style="bold green"))
+    console.print()
+    console.print("  Open this URL in your browser:")
+    console.print()
+    console.print(
+        Padding(
+            Text(authorization.verification_uri_complete, style="cyan underline"),
+            (0, 2),
+        )
+    )
+    console.print()
+    console.print("  Confirm this code:")
+    console.print()
+    code = Table.grid()
+    code.add_column(justify="center", width=52)
+    code.add_row(Text(authorization.user_code, style="bold"))
+    console.print(code)
+    console.print()
+    expires_in = _format_duration(authorization.expires_in)
+    console.print(Text(f"The request expires in {expires_in}.", style="dim"))
+    console.print(Text("Press Ctrl-C to cancel.", style="dim"))
+    console.print()
+
+
+def start_device_approval_status(*, json_output: bool) -> Status | None:
+    """Start the terminal spinner while the browser approval is pending."""
+    if json_output:
+        return None
+    status = console.status(
+        "[cyan]Waiting for approval in your browser[/cyan]",
+        spinner="dots",
+        spinner_style="cyan",
+    )
+    status.start()
+    return status
+
+
+def stop_device_approval_status(status: Status | None) -> None:
+    """Stop a device approval spinner when one is active."""
+    if status is not None:
+        status.stop()
+
+
+def emit_identity(
+    command: Literal["login", "whoami"],
+    user: HorizonUser,
+    *,
+    json_output: bool,
+) -> None:
+    """Show the authenticated user."""
+    if json_output:
+        _write_json(
+            {
+                "ok": True,
+                "command": command,
+                "user": user.model_dump(mode="json"),
+            }
+        )
+        return
+
+    console.print()
+    if command == "login":
+        panel = _account_panel(
+            user,
+            title="Logged into Horizon",
+            message="You are signed in to FastMCP.",
+        )
+    else:
+        panel = _account_panel(
+            user,
+            title="Horizon Account",
+            message="● Signed in",
+        )
+    console.print(panel)
+    console.print()
+
+
+def emit_environment_logout(*, json_output: bool) -> None:
+    """Explain why logout cannot change an environment credential."""
+    if json_output:
+        _write_json(
+            {
+                "ok": True,
+                "command": "logout",
+                "credentialSource": "environment",
+                "localCredentialRemoved": False,
+                "remoteRevoked": False,
+            }
+        )
+        return
+
+    message = Group(
+        Text("This session uses HORIZON_API_KEY.", style="bold"),
+        Text("Remove it from your environment to sign out."),
+        Text("No credential was revoked or removed.", style="dim"),
+    )
+    console.print()
+    console.print(
+        Panel(
+            message,
+            title=Text("Horizon Account", style="bold cyan"),
+            title_align="left",
+            box=box.ROUNDED,
+            border_style="cyan",
+            padding=(1, 2),
+            width=60,
+        )
+    )
+    console.print()
+
+
+def emit_logout(
+    *,
+    remote_revoked: bool,
+    json_output: bool,
+) -> None:
+    """Show a successful local logout result."""
+    if json_output:
+        _write_json(
+            {
+                "ok": True,
+                "command": "logout",
+                "localCredentialRemoved": True,
+                "remoteRevoked": remote_revoked,
+            }
+        )
+        return
+
+    if remote_revoked:
+        title = "Logged out of Horizon"
+        message = "The Horizon credential was revoked and removed from this device."
+        style = "green"
+    else:
+        title = "Horizon Account"
+        message = "No active Horizon credential remains on this device."
+        style = "cyan"
+
+    console.print()
+    console.print(
+        Panel(
+            Text(message),
+            title=Text(title, style=f"bold {style}"),
+            title_align="left",
+            box=box.ROUNDED,
+            border_style=style,
+            padding=(1, 2),
+            width=60,
+        )
+    )
+    console.print()
+
+
+def emit_error(
+    command: CommandName,
+    category: ErrorCategory,
+    message: str,
+    *,
+    json_output: bool,
+    details: dict[str, object] | None = None,
+) -> None:
+    """Show a stable expected command failure."""
+    if json_output:
+        payload: dict[str, object] = {
+            "ok": False,
+            "command": command,
+            "error": {
+                "category": category,
+                "message": message,
+            },
+        }
+        if details:
+            payload.update(details)
+        _write_json(payload)
+        return
+
+    titles = {
+        "login": "✗ Sign in failed",
+        "logout": "✗ Sign out failed",
+        "whoami": "✗ Account lookup failed",
+    }
+    error_console.print()
+    error_console.print(
+        Panel(
+            Text(message),
+            title=Text(titles[command], style="bold red"),
+            title_align="left",
+            box=box.ROUNDED,
+            border_style="red",
+            padding=(1, 2),
+            width=60,
+        )
+    )
+    error_console.print()

tests/cli/deploy/test_command.py

@@ -0,0 +1,462 @@
+import json
+from collections.abc import Callable, Iterator
+from contextlib import contextmanager
+from pathlib import Path
+from unittest.mock import Mock
+from urllib.parse import parse_qs
+
+import httpx2
+import pytest
+from pydantic import SecretStr
+
+import fastmcp
+import fastmcp.cli.deploy.authentication as authentication_module
+import fastmcp.cli.deploy.command as command_module
+from fastmcp.cli.deploy.command import login, logout, whoami
+from fastmcp.cli.deploy.configuration import ConfigurationStore
+from fastmcp.cli.deploy.credentials import CredentialStore
+from fastmcp.cli.deploy.horizon_client import HorizonClient
+from fastmcp.cli.deploy.state import StateFileError
+
+
+class HorizonAuthAPI:
+    def __init__(
+        self,
+        *,
+        token_error: str | None = None,
+        revoke_status: int = 204,
+        invalid_api_key: str | None = None,
+        on_request: Callable[[httpx2.Request], None] | None = None,
+    ) -> None:
+        self.token_error = token_error
+        self.revoke_status = revoke_status
+        self.invalid_api_key = invalid_api_key
+        self.on_request = on_request
+        self.requests: list[httpx2.Request] = []
+
+    def __call__(self, request: httpx2.Request) -> httpx2.Response:
+        self.requests.append(request)
+        if self.on_request is not None:
+            self.on_request(request)
+        path = request.url.path
+        if path == "/api/v0/oauth/device/authorization":
+            return httpx2.Response(
+                200,
+                json={
+                    "device_code": "device-secret",
+                    "user_code": "ABCD-EFGH",
+                    "verification_uri": "https://horizon.prefect.io/oauth/device",
+                    "verification_uri_complete": (
+                        "https://horizon.prefect.io/oauth/device?user_code=ABCD-EFGH"
+                    ),
+                    "expires_in": 600,
+                    "interval": 1,
+                },
+            )
+        if path == "/api/v0/oauth/device/token":
+            if self.token_error is not None:
+                return httpx2.Response(400, json={"error": self.token_error})
+            return httpx2.Response(
+                200,
+                json={"access_token": "fmcp_device_key", "token_type": "Bearer"},
+            )
+        if path == "/api/v0/me":
+            if request.headers.get("Authorization") == (
+                f"Bearer {self.invalid_api_key}"
+            ):
+                return httpx2.Response(401)
+            return httpx2.Response(
+                200,
+                json={
+                    "user": {
+                        "id": "user-1",
+                        "email": "ada@example.com",
+                        "name": "Ada",
+                    }
+                },
+            )
+        if path == "/api/v0/me/api-key":
+            return httpx2.Response(self.revoke_status)
+        raise AssertionError(f"Unexpected request: {request.method} {path}")
+
+
+@pytest.fixture
+def use_horizon_api(
+    monkeypatch: pytest.MonkeyPatch,
+) -> Callable[[HorizonAuthAPI], None]:
+    def use(api: HorizonAuthAPI) -> None:
+        transport = httpx2.MockTransport(api)
+
+        def client(
+            api_origin: str,
+            *,
+            api_key: SecretStr | str | None = None,
+        ) -> HorizonClient:
+            return HorizonClient(
+                api_origin,
+                api_key=api_key,
+                transport=transport,
+            )
+
+        monkeypatch.setattr(command_module, "HorizonClient", client)
+
+    return use
+
+
+def test_session_snapshot_reads_host_and_credential_under_one_lock(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    events: list[str] = []
+    configuration_load = ConfigurationStore.load
+    credential_load = CredentialStore.load
+
+    @contextmanager
+    def lock(directory: Path) -> Iterator[None]:
+        events.append("lock")
+        yield
+        events.append("unlock")
+
+    def load_configuration(store: ConfigurationStore):
+        events.append("configuration")
+        return configuration_load(store)
+
+    def load_credential(store: CredentialStore):
+        events.append("credential")
+        return credential_load(store)
+
+    monkeypatch.setattr(command_module, "state_lock", lock)
+    monkeypatch.setattr(ConfigurationStore, "load", load_configuration)
+    monkeypatch.setattr(CredentialStore, "load", load_credential)
+
+    configuration, credential = command_module._load_session_snapshot(CredentialStore())
+
+    assert configuration.api_origin == "https://horizon.prefect.io"
+    assert credential is None
+    assert events == ["lock", "configuration", "credential", "unlock"]
+
+
+@pytest.fixture(autouse=True)
+def no_device_poll_delay(monkeypatch: pytest.MonkeyPatch) -> None:
+    async def sleep(_: float) -> None:
+        return None
+
+    monkeypatch.setattr(authentication_module.asyncio, "sleep", sleep)
+
+
+async def test_json_login_writes_one_result_and_challenge_to_stderr(
+    use_horizon_api: Callable[[HorizonAuthAPI], None],
+    capsys: pytest.CaptureFixture[str],
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    api = HorizonAuthAPI()
+    use_horizon_api(api)
+    browser_open = Mock()
+    monkeypatch.setattr(command_module.webbrowser, "open", browser_open)
+    monkeypatch.setattr(command_module.platform, "node", lambda: "Avery's laptop")
+    monkeypatch.setattr(command_module.platform, "system", lambda: "Darwin")
+    monkeypatch.setattr(command_module.platform, "machine", lambda: "arm64")
+    monkeypatch.setattr(command_module.fastmcp, "__version__", "4.0.0")
+
+    await login(json_output=True)
+
+    captured = capsys.readouterr()
+    stdout_lines = captured.out.strip().splitlines()
+    assert len(stdout_lines) == 1
+    assert json.loads(stdout_lines[0]) == {
+        "ok": True,
+        "command": "login",
+        "user": {
+            "id": "user-1",
+            "email": "ada@example.com",
+            "name": "Ada",
+        },
+    }
+    assert json.loads(captured.err) == {
+        "event": "device_authorization",
+        "verificationUrl": "https://horizon.prefect.io/oauth/device",
+        "verificationUrlComplete": (
+            "https://horizon.prefect.io/oauth/device?user_code=ABCD-EFGH"
+        ),
+        "userCode": "ABCD-EFGH",
+    }
+    browser_open.assert_not_called()
+    authorization_request = next(
+        request
+        for request in api.requests
+        if request.url.path == "/api/v0/oauth/device/authorization"
+    )
+    assert parse_qs(authorization_request.content.decode()) == {
+        "client_id": ["fastmcp-cli"],
+        "device_name": ["Avery's laptop"],
+        "platform": ["darwin"],
+        "architecture": ["arm64"],
+        "client_version": ["4.0.0"],
+    }
+
+    state = json.loads(CredentialStore().path.read_text())
+    assert state == {"schemaVersion": 1, "apiKey": "fmcp_device_key"}
+    assert not (fastmcp.settings.home / "cli" / "config.json").exists()
+
+
+async def test_login_host_is_saved_before_device_authorization(
+    use_horizon_api: Callable[[HorizonAuthAPI], None],
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    api = HorizonAuthAPI()
+    use_horizon_api(api)
+
+    await login(host="https://dev.horizon.prefect.io/", json_output=True)
+
+    assert json.loads(capsys.readouterr().out)["ok"] is True
+    configuration_path = fastmcp.settings.home / "cli" / "config.json"
+    assert json.loads(configuration_path.read_text()) == {
+        "schemaVersion": 1,
+        "apiOrigin": "https://dev.horizon.prefect.io",
+    }
+    assert {request.url.host for request in api.requests} == {"dev.horizon.prefect.io"}
+
+
+async def test_login_rejects_an_invalid_host(
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    with pytest.raises(SystemExit, match="1"):
+        await login(host="https://horizon.prefect.io/path", json_output=True)
+
+    result = json.loads(capsys.readouterr().out)
+    assert result["error"]["category"] == "invalid_host"
+    assert CredentialStore().path.exists() is False
+
+
+async def test_tty_login_survives_browser_open_failure(
+    use_horizon_api: Callable[[HorizonAuthAPI], None],
+    capsys: pytest.CaptureFixture[str],
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    use_horizon_api(HorizonAuthAPI())
+    browser_open = Mock(side_effect=OSError("No browser"))
+    monkeypatch.setattr(command_module, "_can_open_browser", lambda: True)
+    monkeypatch.setattr(command_module.webbrowser, "open", browser_open)
+
+    await login()
+
+    output = capsys.readouterr().out
+    assert "https://horizon.prefect.io/oauth/device" in output
+    assert "ABCD-EFGH" in output
+    assert "Logged into Horizon" in output
+    assert "Ada" in output
+    assert "ada@example.com" in output
+    assert "Organization" not in output
+    browser_open.assert_called_once()
+
+
+async def test_whoami_uses_the_stored_key_after_a_restart(
+    use_horizon_api: Callable[[HorizonAuthAPI], None],
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    api = HorizonAuthAPI()
+    use_horizon_api(api)
+    await login(json_output=True)
+    capsys.readouterr()
+
+    await whoami(json_output=True)
+
+    result = json.loads(capsys.readouterr().out)
+    assert result["command"] == "whoami"
+    assert result["user"]["email"] == "ada@example.com"
+    assert [request.url.path for request in api.requests].count("/api/v0/me") == 2
+
+
+async def test_login_replaces_an_invalid_stored_key(
+    use_horizon_api: Callable[[HorizonAuthAPI], None],
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    use_horizon_api(HorizonAuthAPI(invalid_api_key="fmcp_stale_key"))
+    CredentialStore().save("fmcp_stale_key")
+
+    await login(json_output=True)
+
+    captured = capsys.readouterr()
+    assert json.loads(captured.out)["ok"] is True
+    assert json.loads(captured.err)["event"] == "device_authorization"
+    stored_key = CredentialStore().load()
+    assert stored_key is not None
+    assert stored_key.get_secret_value() == "fmcp_device_key"
+
+
+async def test_login_never_persists_an_environment_key(
+    use_horizon_api: Callable[[HorizonAuthAPI], None],
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    api = HorizonAuthAPI()
+    use_horizon_api(api)
+    monkeypatch.setenv("HORIZON_API_KEY", "fmcp_environment_key")
+
+    await login(json_output=True)
+
+    assert CredentialStore().path.exists() is False
+    assert not any(
+        request.url.path.startswith("/api/v0/oauth/device") for request in api.requests
+    )
+
+
+async def test_json_whoami_reports_a_failed_rejected_key_cleanup(
+    use_horizon_api: Callable[[HorizonAuthAPI], None],
+    capsys: pytest.CaptureFixture[str],
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    use_horizon_api(HorizonAuthAPI(invalid_api_key="fmcp_stale_key"))
+    CredentialStore().save("fmcp_stale_key")
+
+    def fail_clear(store: CredentialStore) -> None:
+        raise StateFileError("cleanup failed")
+
+    monkeypatch.setattr(CredentialStore, "clear", fail_clear)
+
+    with pytest.raises(SystemExit, match="1"):
+        await whoami(json_output=True)
+
+    result = json.loads(capsys.readouterr().out)
+    assert result["error"]["category"] == "state_error"
+
+
+async def test_whoami_does_not_clear_a_newer_host_credential(
+    use_horizon_api: Callable[[HorizonAuthAPI], None],
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    credentials = CredentialStore()
+    credentials.save("fmcp_stale_key")
+    switched = False
+
+    def switch_host(request: httpx2.Request) -> None:
+        nonlocal switched
+        if request.url.path != "/api/v0/me" or switched:
+            return
+        switched = True
+        ConfigurationStore().set_api_origin(
+            "https://dev.horizon.prefect.io",
+            credentials=credentials,
+        )
+        credentials.save_for_origin(
+            "fmcp_new_key",
+            expected_api_origin="https://dev.horizon.prefect.io",
+        )
+
+    api = HorizonAuthAPI(
+        invalid_api_key="fmcp_stale_key",
+        on_request=switch_host,
+    )
+    use_horizon_api(api)
+
+    with pytest.raises(SystemExit, match="1"):
+        await whoami(json_output=True)
+
+    result = json.loads(capsys.readouterr().out)
+    assert result["error"]["category"] == "authentication_invalid"
+    assert ConfigurationStore().load().api_origin == ("https://dev.horizon.prefect.io")
+    stored_key = credentials.load()
+    assert stored_key is not None
+    assert stored_key.get_secret_value() == "fmcp_new_key"
+    assert api.requests[0].url.host == "horizon.prefect.io"
+
+
+async def test_json_whoami_does_not_start_device_authorization(
+    capsys: pytest.CaptureFixture[str],
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    browser_open = Mock()
+    monkeypatch.setattr(command_module.webbrowser, "open", browser_open)
+
+    with pytest.raises(SystemExit, match="1"):
+        await whoami(json_output=True)
+
+    result = json.loads(capsys.readouterr().out)
+    assert result["error"]["category"] == "authentication_required"
+    browser_open.assert_not_called()
+
+
+@pytest.mark.parametrize(
+    ("token_error", "category"),
+    [
+        ("access_denied", "authorization_denied"),
+        ("expired_token", "authorization_expired"),
+    ],
+)
+async def test_json_login_reports_stable_device_failures(
+    token_error: str,
+    category: str,
+    use_horizon_api: Callable[[HorizonAuthAPI], None],
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    use_horizon_api(HorizonAuthAPI(token_error=token_error))
+
+    with pytest.raises(SystemExit, match="1"):
+        await login(json_output=True)
+
+    result = json.loads(capsys.readouterr().out)
+    assert result["error"]["category"] == category
+    assert CredentialStore().path.exists() is False
+
+
+async def test_logout_does_not_modify_environment_or_stored_credentials(
+    use_horizon_api: Callable[[HorizonAuthAPI], None],
+    capsys: pytest.CaptureFixture[str],
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    api = HorizonAuthAPI()
+    use_horizon_api(api)
+    monkeypatch.setenv("HORIZON_API_KEY", "fmcp_environment_key")
+    CredentialStore().save("fmcp_stored_key")
+
+    await logout(json_output=True)
+
+    assert json.loads(capsys.readouterr().out) == {
+        "ok": True,
+        "command": "logout",
+        "credentialSource": "environment",
+        "localCredentialRemoved": False,
+        "remoteRevoked": False,
+    }
+    stored_key = CredentialStore().load()
+    assert stored_key is not None
+    assert stored_key.get_secret_value() == "fmcp_stored_key"
+    assert api.requests == []
+
+
+async def test_logout_revokes_the_remote_key_and_clears_local_state(
+    use_horizon_api: Callable[[HorizonAuthAPI], None],
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    api = HorizonAuthAPI()
+    use_horizon_api(api)
+    CredentialStore().save("fmcp_stored_key")
+
+    await logout(json_output=True)
+
+    assert json.loads(capsys.readouterr().out) == {
+        "ok": True,
+        "command": "logout",
+        "localCredentialRemoved": True,
+        "remoteRevoked": True,
+    }
+    assert CredentialStore().path.exists() is False
+    assert any(
+        request.method == "DELETE" and request.url.path == "/api/v0/me/api-key"
+        for request in api.requests
+    )
+
+
+async def test_logout_clears_local_state_when_remote_revocation_fails(
+    use_horizon_api: Callable[[HorizonAuthAPI], None],
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    use_horizon_api(HorizonAuthAPI(revoke_status=503))
+    CredentialStore().save("fmcp_stored_key")
+
+    with pytest.raises(SystemExit, match="1"):
+        await logout(json_output=True)
+
+    result = json.loads(capsys.readouterr().out)
+    assert result["error"]["category"] == "remote_revocation_failed"
+    assert result["localCredentialRemoved"] is True
+    assert result["remoteCredentialMayRemain"] is True
+    assert CredentialStore().path.exists() is False

tests/cli/deploy/test_credentials.py

@@ -183,6 +183,29 @@ async def test_interactive_credential_rejects_an_origin_change(
     assert store.load() is None
 
 
+def test_conditional_clear_preserves_newer_state(tmp_path: Path) -> None:
+    store = CredentialStore(tmp_path)
+    store.save("fmcp_current")
+
+    store.clear_if_matches(
+        "fmcp_different",
+        expected_api_origin="https://horizon.prefect.io",
+    )
+    store.clear_if_matches(
+        "fmcp_current",
+        expected_api_origin="https://dev.horizon.prefect.io",
+    )
+
+    assert load_secret(store).get_secret_value() == "fmcp_current"
+
+    store.clear_if_matches(
+        "fmcp_current",
+        expected_api_origin="https://horizon.prefect.io",
+    )
+
+    assert store.load() is None
+
+
 async def test_missing_noninteractive_credential_is_explicit(tmp_path: Path) -> None:
     with pytest.raises(AuthenticationRequiredError):
         await resolve_credential(CredentialStore(tmp_path), environ={})

tests/cli/deploy/test_output.py

@@ -0,0 +1,167 @@
+import json
+
+import pytest
+
+from fastmcp.cli.deploy.horizon_client import DeviceAuthorization, HorizonUser
+from fastmcp.cli.deploy.output import (
+    emit_device_challenge,
+    emit_environment_logout,
+    emit_error,
+    emit_identity,
+    emit_logout,
+)
+
+
+def authorization() -> DeviceAuthorization:
+    return DeviceAuthorization(
+        device_code="device-secret",
+        user_code="ABCD-EFGH",
+        verification_uri="https://horizon.prefect.io/oauth/device",
+        verification_uri_complete=(
+            "https://horizon.prefect.io/oauth/device?user_code=ABCD-EFGH"
+        ),
+        expires_in=600,
+        interval=5,
+    )
+
+
+def user() -> HorizonUser:
+    return HorizonUser(id="user-1", email="ada@example.com", name="Ada")
+
+
+def test_json_device_challenge_uses_only_stderr(
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    emit_device_challenge(authorization(), json_output=True)
+
+    captured = capsys.readouterr()
+    assert captured.out == ""
+    assert json.loads(captured.err) == {
+        "event": "device_authorization",
+        "verificationUrl": "https://horizon.prefect.io/oauth/device",
+        "verificationUrlComplete": (
+            "https://horizon.prefect.io/oauth/device?user_code=ABCD-EFGH"
+        ),
+        "userCode": "ABCD-EFGH",
+    }
+
+
+def test_tty_device_challenge_uses_the_sign_in_layout(
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    emit_device_challenge(authorization(), json_output=False)
+
+    output = capsys.readouterr().out
+    assert "│" in output
+    assert "Deploy FastMCP on Horizon" in output
+    assert "✓ Device authorization started" in output
+    assert "https://horizon.prefect.io/oauth/device?user_code=ABCD-EFGH" in output
+    assert "ABCD-EFGH" in output
+    assert "The request expires in 10 minutes." in output
+
+
+def test_json_identity_has_stable_fields(
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    emit_identity("login", user(), json_output=True)
+
+    result = json.loads(capsys.readouterr().out)
+    assert result == {
+        "ok": True,
+        "command": "login",
+        "user": {
+            "id": "user-1",
+            "email": "ada@example.com",
+            "name": "Ada",
+        },
+    }
+
+
+def test_tty_identity_uses_an_account_panel(
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    emit_identity("whoami", user(), json_output=False)
+
+    output = capsys.readouterr().out
+    assert "│" in output
+    assert "Horizon Account" in output
+    assert "Ada" in output
+    assert "ada@example.com" in output
+    assert "● Signed in" in output
+    assert "Organization" not in output
+
+
+def test_json_error_has_stable_fields(
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    emit_error(
+        "logout",
+        "remote_revocation_failed",
+        "The remote key can remain active.",
+        json_output=True,
+        details={
+            "localCredentialRemoved": True,
+            "remoteCredentialMayRemain": True,
+        },
+    )
+
+    result = json.loads(capsys.readouterr().out)
+    assert result == {
+        "ok": False,
+        "command": "logout",
+        "error": {
+            "category": "remote_revocation_failed",
+            "message": "The remote key can remain active.",
+        },
+        "localCredentialRemoved": True,
+        "remoteCredentialMayRemain": True,
+    }
+
+
+def test_tty_environment_logout_explains_that_no_action_was_taken(
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    emit_environment_logout(json_output=False)
+
+    output = capsys.readouterr().out
+    assert "Horizon Account" in output
+    assert "This session uses HORIZON_API_KEY." in output
+    assert "Remove it from your environment to sign out." in output
+    assert "No credential was revoked or removed." in output
+
+
+def test_json_environment_logout_has_stable_fields(
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    emit_environment_logout(json_output=True)
+
+    assert json.loads(capsys.readouterr().out) == {
+        "ok": True,
+        "command": "logout",
+        "credentialSource": "environment",
+        "localCredentialRemoved": False,
+        "remoteRevoked": False,
+    }
+
+
+def test_tty_logout_uses_the_horizon_header(
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    emit_logout(remote_revoked=True, json_output=False)
+
+    output = capsys.readouterr().out
+    assert "Logged out of Horizon" in output
+    assert "│" in output
+
+
+def test_json_logout_has_stable_fields(
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    emit_logout(remote_revoked=True, json_output=True)
+
+    assert json.loads(capsys.readouterr().out) == {
+        "ok": True,
+        "command": "logout",
+        "localCredentialRemoved": True,
+        "remoteRevoked": True,
+    }

tests/cli/test_cli.py

@@ -35,6 +35,20 @@ class TestMainCLI:
         assert isinstance(exc_info.value, SystemExit)
         assert exc_info.value.code == 1
 
+    @pytest.mark.parametrize("name", ["login", "logout", "whoami"])
+    def test_horizon_account_commands_are_top_level(self, name: str):
+        command, bound, _ = app.parse_args([name, "--json"])
+
+        assert command.__name__ == name  # type: ignore[attr-defined]  # ty:ignore[unresolved-attribute]
+        assert bound.arguments == {"json_output": True}
+
+    def test_login_accepts_a_horizon_host(self):
+        _, bound, _ = app.parse_args(
+            ["login", "--host", "https://dev.horizon.prefect.io"]
+        )
+
+        assert bound.arguments == {"host": "https://dev.horizon.prefect.io"}
+
 
 class TestVersionCommand:
     """Test the version command."""