mcp: add client-side OAuth flow #544
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,107 @@ | ||
| // Copyright 2025 The Go MCP SDK Authors. All rights reserved. | ||
| // Use of this source code is governed by an MIT-style | ||
| // license that can be found in the LICENSE file. | ||
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| //go:build mcp_go_client_oauth | ||
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| package auth | ||
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| import ( | ||
| "context" | ||
| "errors" | ||
| "net/http" | ||
| "sync" | ||
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| "github.com/modelcontextprotocol/go-sdk/internal/oauthex" | ||
| "golang.org/x/oauth2" | ||
| ) | ||
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| // An OAuthHandler conducts an OAuth flow and returns a [oauth2.TokenSource] if the authorization | ||
| // is approved, or an error if not. | ||
| type OAuthHandler func(context.Context, OAuthHandlerArgs) (oauth2.TokenSource, error) | ||
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| // OAuthHandlerArgs are arguments to an [OAuthHandler]. | ||
| type OAuthHandlerArgs struct { | ||
| // The URL to fetch protected resource metadata, extracted from the WWW-Authenticate header. | ||
| // Empty if not present or there was an error obtaining it. | ||
| ResourceMetadataURL string | ||
| } | ||
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| // HTTPTransport is an [http.RoundTripper] that follows the MCP | ||
| // OAuth protocol when it encounters a 401 Unauthorized response. | ||
| type HTTPTransport struct { | ||
| handler OAuthHandler | ||
| mu sync.Mutex // protects opts.Base | ||
| opts HTTPTransportOptions | ||
| } | ||
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| // NewHTTPTransport returns a new [*HTTPTransport]. | ||
| // The handler is invoked when an HTTP request results in a 401 Unauthorized status. | ||
| // It is called only once per transport. Once a TokenSource is obtained, it is used | ||
| // for the lifetime of the transport; subsequent 401s are not processed. | ||
| func NewHTTPTransport(handler OAuthHandler, opts *HTTPTransportOptions) (*HTTPTransport, error) { | ||
| if handler == nil { | ||
| return nil, errors.New("handler cannot be nil") | ||
| } | ||
| t := &HTTPTransport{ | ||
| handler: handler, | ||
| } | ||
| if opts != nil { | ||
| t.opts = *opts | ||
| } | ||
| if t.opts.Base == nil { | ||
| t.opts.Base = http.DefaultTransport | ||
| } | ||
| return t, nil | ||
| } | ||
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| // HTTPTransportOptions are options to [NewHTTPTransport]. | ||
| type HTTPTransportOptions struct { | ||
| // Base is the [http.RoundTripper] to use. | ||
| // If nil, [http.DefaultTransport] is used. | ||
| Base http.RoundTripper | ||
| } | ||
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| func (t *HTTPTransport) RoundTrip(req *http.Request) (*http.Response, error) { | ||
| t.mu.Lock() | ||
| base := t.opts.Base | ||
| t.mu.Unlock() | ||
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| resp, err := base.RoundTrip(req) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| if resp.StatusCode != http.StatusUnauthorized { | ||
| return resp, nil | ||
| } | ||
| if _, ok := base.(*oauth2.Transport); ok { | ||
| // We failed to authorize even with a token source; give up. | ||
| return resp, nil | ||
| } | ||
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| resp.Body.Close() | ||
| // Try to authorize. | ||
| t.mu.Lock() | ||
| defer t.mu.Unlock() | ||
| // If we don't have a token source, get one by following the OAuth flow. | ||
| // (We may have obtained one while t.mu was not held above.) | ||
| if _, ok := t.opts.Base.(*oauth2.Transport); !ok { | ||
| authHeaders := resp.Header[http.CanonicalHeaderKey("WWW-Authenticate")] | ||
| ts, err := t.handler(req.Context(), OAuthHandlerArgs{ | ||
| ResourceMetadataURL: extractResourceMetadataURL(authHeaders), | ||
| }) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| t.opts.Base = &oauth2.Transport{Base: t.opts.Base, Source: ts} | ||
| } | ||
| return t.opts.Base.RoundTrip(req.Clone(req.Context())) | ||
|
There was a problem hiding this comment. In cagent we use the same trick for OAuth. I just spent the morning debugging and fixing our code for streamable mcp servers and thought I'd tell you what was wrong, might be useful for you. This second request that comes after the oauth flow has a half-broken request, the body of the request was already read by the first call on line 70, so you would get a 400 Bad Request back from the server. You need to hold on the original body and put it back here before sending a second RoundTrip. |
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| } | ||
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| func extractResourceMetadataURL(authHeaders []string) string { | ||
| cs, err := oauthex.ParseWWWAuthenticate(authHeaders) | ||
| if err != nil { | ||
| return "" | ||
| } | ||
| return oauthex.ResourceMetadataURL(cs) | ||
| } | ||
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