fix header auth demo to use correct context API

the demo was using Context.get() which doesn't exist. the correct API is get_context() from fastmcp.server.dependencies.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

repros/header_auth_demo.py

@@ -0,0 +1,161 @@
+"""Demo: Per-request authentication using custom headers in FastMCP
+
+This demonstrates how a centrally hosted MCP server could extract user identity
+from HTTP headers on each request, enabling multi-tenant scenarios where:
+1. Users connect via mcp-remote with custom headers (e.g., --header "X-Prefect-Api-Key: ${API_KEY}")
+2. Server extracts credentials from headers per-request
+3. Server uses those credentials to make authenticated API calls
+
+This is the pattern needed for a globally hosted Prefect MCP where users
+provide their own Prefect API URL/key without deploying their own server.
+"""
+
+from typing import Any
+
+import mcp.types as mt
+
+from fastmcp import FastMCP
+from fastmcp.server.dependencies import get_http_headers
+from fastmcp.server.middleware import CallNext, Middleware, MiddlewareContext
+
+
+# Simulated external API that requires credentials
+class PrefectAPI:
+    """Simulates Prefect API that requires API URL + key"""
+
+    def __init__(self, api_url: str, api_key: str):
+        self.api_url = api_url
+        self.api_key = api_key
+
+    def get_flows(self) -> list[dict]:
+        """Simulated API call"""
+        return [
+            {"id": "flow-1", "name": "ETL Pipeline", "api_url": self.api_url},
+            {"id": "flow-2", "name": "Data Processing", "api_url": self.api_url},
+        ]
+
+
+# Custom middleware that extracts credentials from headers
+class HeaderAuthMiddleware(Middleware):
+    """Extracts authentication info from HTTP headers and makes it available to tools"""
+
+    async def on_call_tool(
+        self,
+        context: MiddlewareContext[mt.CallToolRequestParams],
+        call_next: CallNext[mt.CallToolRequestParams, Any],
+    ) -> Any:
+        # Access the FastMCP context which contains the raw request
+        fastmcp_ctx = context.fastmcp_context
+
+        if fastmcp_ctx:
+            print(f"[Middleware] Processing tool call: {context.message.params.name}")
+
+            # Extract headers using the fastmcp.server.dependencies function
+            try:
+                headers = get_http_headers(include_all=True)
+                print(f"[Middleware] Found {len(headers)} HTTP headers")
+
+                # Extract auth credentials from custom headers
+                api_url = headers.get("x-prefect-api-url")
+                api_key = headers.get("x-prefect-api-key")
+
+                if api_url and api_key:
+                    fastmcp_ctx.set_state(
+                        "auth_info", {"api_url": api_url, "api_key": api_key}
+                    )
+                    print(f"[Middleware] ✅ Extracted auth from headers: {api_url}")
+                else:
+                    print("[Middleware] ⚠️  No auth headers found, using defaults")
+                    # Fallback to simulated values for testing
+                    fastmcp_ctx.set_state(
+                        "auth_info",
+                        {
+                            "api_url": "https://api.prefect.cloud/default",
+                            "api_key": "pnu_simulated_key_no_headers",
+                        },
+                    )
+
+            except RuntimeError as e:
+                # Not running in HTTP mode (e.g., stdio transport)
+                print(f"[Middleware] ⚠️  Not in HTTP mode: {e}")
+                # Set simulated values for stdio testing
+                fastmcp_ctx.set_state(
+                    "auth_info",
+                    {
+                        "api_url": "https://api.prefect.cloud/stdio-mode",
+                        "api_key": "pnu_simulated_key_stdio",
+                    },
+                )
+
+        return await call_next(context)
+
+
+# Create FastMCP app with middleware
+mcp = FastMCP("Header Auth Demo")
+
+# Add the custom middleware
+middleware = HeaderAuthMiddleware()
+mcp.add_middleware(middleware)
+
+
+@mcp.tool()
+def get_my_flows() -> str:
+    """Get flows for the authenticated user (using credentials from request headers)"""
+    from fastmcp.server.dependencies import get_context
+
+    # Access the current request context
+    ctx = get_context()
+
+    # Extract auth info that was set by middleware
+    auth_info = ctx.get_state("auth_info")
+
+    if not auth_info:
+        return "❌ No authentication info found in request headers!"
+
+    # Create API client with per-request credentials
+    api = PrefectAPI(api_url=auth_info["api_url"], api_key=auth_info["api_key"])
+
+    # Make authenticated API call
+    flows = api.get_flows()
+
+    result = (
+        f"✅ Found {len(flows)} flows for user with API URL: {auth_info['api_url']}\n\n"
+    )
+    for flow in flows:
+        result += f"- {flow['name']} (ID: {flow['id']})\n"
+
+    return result
+
+
+@mcp.tool()
+def show_auth_context() -> str:
+    """Show what authentication info was extracted from headers"""
+    from fastmcp.server.dependencies import get_context
+
+    ctx = get_context()
+    auth_info = ctx.get_state("auth_info")
+
+    if not auth_info:
+        return "❌ No authentication info in context"
+
+    return f"""
+✅ Authentication Info Extracted:
+- API URL: {auth_info.get("api_url", "not set")}
+- API Key: {auth_info.get("api_key", "not set")[:20]}... (truncated)
+
+This info would normally come from HTTP headers like:
+  X-Prefect-Api-Url: {auth_info.get("api_url")}
+  X-Prefect-Api-Key: {auth_info.get("api_key")}
+"""
+
+
+if __name__ == "__main__":
+    # Run the server
+    print("\n🚀 Header Auth Demo Server\n")
+    print("This demonstrates per-request authentication via headers.")
+    print("In production, users would connect via mcp-remote with:")
+    print('  --header "X-Prefect-Api-Url: ${PREFECT_API_URL}"')
+    print('  --header "X-Prefect-Api-Key: ${PREFECT_API_KEY}"')
+    print("\n")
+
+    mcp.run()