docs: add bearer auth server example

docs/authorization.md

@@ -1,5 +1,80 @@
 # Authorization
 
-!!! warning "Under Construction"
+MCP servers that expose protected tools can validate bearer tokens by passing a
+`TokenVerifier` and `AuthSettings` when creating the server. The SDK applies the
+same bearer-token middleware to Streamable HTTP and SSE transports, so tool
+handlers do not need to inspect the `Authorization` header themselves.
 
-    This page is currently being written. Check back soon for complete documentation.
+## Bearer Token Server
+
+Use this pattern when you already have bearer tokens from an external
+authorization server, API gateway, or another trusted issuer. The verifier owns
+the token validation logic and returns an `AccessToken` only when the incoming
+token is valid for this MCP server.
+
+```python
+from pydantic import AnyHttpUrl
+
+from mcp.server.auth.provider import AccessToken, TokenVerifier
+from mcp.server.auth.settings import AuthSettings
+from mcp.server.mcpserver import MCPServer
+
+
+class StaticTokenVerifier(TokenVerifier):
+    """Demo verifier. Replace this with your real token validation."""
+
+    async def verify_token(self, token: str) -> AccessToken | None:
+        if token != "dev-token":
+            return None
+
+        return AccessToken(
+            token=token,
+            client_id="local-client",
+            scopes=["tools:read"],
+        )
+
+
+mcp = MCPServer(
+    "Protected Demo",
+    token_verifier=StaticTokenVerifier(),
+    auth=AuthSettings(
+        issuer_url=AnyHttpUrl("https://auth.example.com"),
+        resource_server_url=AnyHttpUrl("http://localhost:8000"),
+        required_scopes=["tools:read"],
+    ),
+)
+
+
+@mcp.tool()
+async def protected_ping() -> str:
+    """Return a message only for authenticated callers."""
+    return "pong"
+
+
+if __name__ == "__main__":
+    mcp.run(transport="sse")
+    # Or use Streamable HTTP:
+    # mcp.run(transport="streamable-http")
+```
+
+Clients must send the token in the HTTP `Authorization` header:
+
+```http
+Authorization: Bearer dev-token
+```
+
+For the MCP Inspector, choose the matching transport, point it at the server
+URL, and enter the bearer token in the Inspector's token field. With the default
+paths, SSE uses `http://localhost:8000/sse` and Streamable HTTP uses
+`http://localhost:8000/mcp`.
+
+If the token is missing or invalid, the SDK returns `401 invalid_token`. If the
+token is valid but does not include every `required_scopes` entry, the SDK
+returns `403 insufficient_scope`.
+
+!!! note
+
+    The token string above is only a local development placeholder. Production
+    verifiers should validate signed tokens, introspect opaque tokens, or call
+    the appropriate authorization service instead of comparing against a hard
+    coded value.