Fix passing token string to client auth

src/fastmcp/client/transports.py

@@ -32,6 +32,7 @@ from mcp.shared.memory import create_connected_server_and_client_session
 from pydantic import AnyUrl
 from typing_extensions import Unpack
 
+from fastmcp.client.auth.bearer import BearerAuth
 from fastmcp.client.auth.oauth import OAuth
 from fastmcp.server.dependencies import get_http_headers
 from fastmcp.server.server import FastMCP
@@ -152,7 +153,7 @@ class WSTransport(ClientTransport):
                 yield session
 
     def __repr__(self) -> str:
-        return f"<WebSocket(url='{self.url}')>"
+        return f"<WebSocketTransport(url='{self.url}')>"
 
 
 class SSETransport(ClientTransport):
@@ -183,8 +184,7 @@ class SSETransport(ClientTransport):
         if auth == "oauth":
             auth = OAuth(self.url)
         elif isinstance(auth, str):
-            self.headers["Authorization"] = auth
-            auth = None
+            auth = BearerAuth(auth)
         self.auth = auth
 
     @contextlib.asynccontextmanager
@@ -221,7 +221,7 @@ class SSETransport(ClientTransport):
                 yield session
 
     def __repr__(self) -> str:
-        return f"<SSE(url='{self.url}')>"
+        return f"<SSETransport(url='{self.url}')>"
 
 
 class StreamableHttpTransport(ClientTransport):
@@ -252,8 +252,7 @@ class StreamableHttpTransport(ClientTransport):
         if auth == "oauth":
             auth = OAuth(self.url)
         elif isinstance(auth, str):
-            self.headers["Authorization"] = auth
-            auth = None
+            auth = BearerAuth(auth)
         self.auth = auth
 
     @contextlib.asynccontextmanager
@@ -291,7 +290,7 @@ class StreamableHttpTransport(ClientTransport):
                 yield session
 
     def __repr__(self) -> str:
-        return f"<StreamableHttp(url='{self.url}')>"
+        return f"<StreamableHttpTransport(url='{self.url}')>"
 
 
 class StdioTransport(ClientTransport):
@@ -683,7 +682,7 @@ class FastMCPTransport(ClientTransport):
             yield session
 
     def __repr__(self) -> str:
-        return f"<FastMCP(server='{self.server.name}')>"
+        return f"<FastMCPTransport(server='{self.server.name}')>"
 
 
 class MCPConfigTransport(ClientTransport):
@@ -769,7 +768,7 @@ class MCPConfigTransport(ClientTransport):
             yield session
 
     def __repr__(self) -> str:
-        return f"<MCPConfig(config='{self.config}')>"
+        return f"<MCPConfigTransport(config='{self.config}')>"
 
 
 @overload

tests/client/test_client.py

@@ -4,9 +4,11 @@ from typing import cast
 
 import pytest
 from mcp import McpError
+from mcp.client.auth import OAuthClientProvider
 from pydantic import AnyUrl
 
 from fastmcp.client import Client
+from fastmcp.client.auth.bearer import BearerAuth
 from fastmcp.client.transports import (
     FastMCPTransport,
     MCPConfigTransport,
@@ -810,3 +812,73 @@ class TestInferTransport:
         server = FastMCP1()
         transport = infer_transport(server)
         assert isinstance(transport, FastMCPTransport)
+
+
+class TestAuth:
+    def test_default_auth_is_none(self):
+        client = Client(transport=StreamableHttpTransport("http://localhost:8000"))
+        assert client.transport.auth is None
+
+    def test_stdio_doesnt_support_auth(self):
+        with pytest.raises(ValueError, match="This transport does not support auth"):
+            Client(transport=StdioTransport("echo", ["hello"]), auth="oauth")
+
+    def test_oauth_literal_sets_up_oauth_shttp(self):
+        client = Client(
+            transport=StreamableHttpTransport("http://localhost:8000"), auth="oauth"
+        )
+        assert isinstance(client.transport, StreamableHttpTransport)
+        assert isinstance(client.transport.auth, OAuthClientProvider)
+
+    def test_oauth_literal_pass_direct_to_transport(self):
+        client = Client(
+            transport=StreamableHttpTransport("http://localhost:8000", auth="oauth"),
+        )
+        assert isinstance(client.transport, StreamableHttpTransport)
+        assert isinstance(client.transport.auth, OAuthClientProvider)
+
+    def test_oauth_literal_sets_up_oauth_sse(self):
+        client = Client(transport=SSETransport("http://localhost:8000"), auth="oauth")
+        assert isinstance(client.transport, SSETransport)
+        assert isinstance(client.transport.auth, OAuthClientProvider)
+
+    def test_oauth_literal_pass_direct_to_transport_sse(self):
+        client = Client(transport=SSETransport("http://localhost:8000", auth="oauth"))
+        assert isinstance(client.transport, SSETransport)
+        assert isinstance(client.transport.auth, OAuthClientProvider)
+
+    def test_auth_string_sets_up_bearer_auth_shttp(self):
+        client = Client(
+            transport=StreamableHttpTransport("http://localhost:8000"),
+            auth="test_token",
+        )
+        assert isinstance(client.transport, StreamableHttpTransport)
+        assert isinstance(client.transport.auth, BearerAuth)
+        assert client.transport.auth.token.get_secret_value() == "test_token"
+
+    def test_auth_string_pass_direct_to_transport_shttp(self):
+        client = Client(
+            transport=StreamableHttpTransport(
+                "http://localhost:8000", auth="test_token"
+            ),
+        )
+        assert isinstance(client.transport, StreamableHttpTransport)
+        assert isinstance(client.transport.auth, BearerAuth)
+        assert client.transport.auth.token.get_secret_value() == "test_token"
+
+    def test_auth_string_sets_up_bearer_auth_sse(self):
+        client = Client(
+            transport=SSETransport("http://localhost:8000"),
+            auth="test_token",
+        )
+        assert isinstance(client.transport, SSETransport)
+        assert isinstance(client.transport.auth, BearerAuth)
+        assert client.transport.auth.token.get_secret_value() == "test_token"
+
+    def test_auth_string_pass_direct_to_transport_sse(self):
+        client = Client(
+            transport=SSETransport("http://localhost:8000", auth="test_token"),
+        )
+        assert isinstance(client.transport, SSETransport)
+        assert isinstance(client.transport.auth, BearerAuth)
+        assert client.transport.auth.token.get_secret_value() == "test_token"

tests/server/test_proxy.py

@@ -9,7 +9,7 @@ from pydantic import AnyUrl
 
 from fastmcp import FastMCP
 from fastmcp.client import Client
-from fastmcp.client.transports import FastMCPTransport
+from fastmcp.client.transports import FastMCPTransport, StreamableHttpTransport
 from fastmcp.exceptions import ToolError
 from fastmcp.server.proxy import FastMCPProxy
 
@@ -104,7 +104,8 @@ def test_as_proxy_with_url():
     """FastMCP.as_proxy should accept a URL without connecting."""
     proxy = FastMCP.as_proxy("http://example.com/mcp")
     assert isinstance(proxy, FastMCPProxy)
-    assert repr(proxy.client.transport).startswith("<StreamableHttp(")
+    assert isinstance(proxy.client.transport, StreamableHttpTransport)
+    assert proxy.client.transport.url == "http://example.com/mcp"
 
 
 class TestTools: