c9317fb5b7This PR introduces client-side OAuth support. # Overall design philosophy The main new interface introduced to support client-side OAuth is the `OAuthHandler`. Contrary to its counter-parts in some other SDKs, it is intentionally small and generic so that it can support most of the OAuth authorization flow variants. The main `mcp` package purposefully delegates almost all auth handling to `OAuthHandler` implementations. This way, the `mcp` package continues to be largely OAuth agnostic. The `auth` package comes with a default `OAuthHandler` implementation – `AuthorizationCodeHandler`, which implements the authorization flow for the `authorization_code` grant type, as defined in the [MCP specification](https://modelcontextprotocol.io/specification/2025-11-25/basic/authorization). It is expected that the `OAuthHandler` implementation granularity will be roughly per grant type, as this parameter influences the authorization flow the most. # Detailed design ## `OAuthHandler` (auth/client.go) The main interface for the integration consists of two methods: ```go type OAuthHandler interface { // TokenSource returns a token source to be used for outgoing requests. // Returned token source might be nil. In that case, the transport will not // add any authorization headers to the request. TokenSource(context.Context) (oauth2.TokenSource, error) // Authorize is called when an HTTP request results in an error that may // be addressed by the authorization flow (currently 401 Unauthorized and 403 Forbidden). // It is responsible for performing the OAuth flow to obtain an access token. // The arguments are the request that failed and the response that was received for it. // The headers of the request are available, but the body will have already been consumed // when Authorize is called. // If the returned error is nil, TokenSource is expected to return a non-nil token source. // After a successful call to Authorize, the HTTP request will be retried by the transport. // The function is responsible for closing the response body. Authorize(context.Context, *http.Request, *http.Response) error } ``` `StreamableClientTransport` accepts this interface as a field and uses the `TokenSource` method to add an `Authorization: Bearer` header to outgoing requests to the MCP server. If the request fails with `401: Unauthorized` or `403: Forbidden`, the transport calls `Authorize` to perform the authorization flow. If `Authorize` returns a non-nil error, the request is retried once. `Authorize` errors do not result in termination of the client session (unless they happen during connection initialization), as some OAuth flows are multi-legged and it should be acceptable to retry for example when the authorization grant was received. *Note:* There was already an `OAuthHandler` type defined as part of a previous iteration of OAuth support. It was renamed to `OAuthHandlerLegacy`. This is the only backwards incompatible API change in the experimental client `auth` part (protected by the `mcp_go_client_oauth` Go build tag). The cost of replacing previous usages is deemed worthwhile to maintain clear naming, under the assumption that the experimental client `auth` part was not widely used. ## `AuthorizationCodeHandler` (auth/authorization_code.go) This is the `OAuthHandler` implementation that fulfills the [MCP specification](https://modelcontextprotocol.io/specification/2025-11-25/basic/authorization). In particular, in supports: - Protected Resource Metadata discovery and fetching - Authorization Server Metadata discovery and fetching - Client registration - OpenID Connect metadata document - Pre-registration - Dynamic Client Registration - PKCE - `client_secret_post`, `client_secret_basic` token endpoint auth methods - Automatic refresh of tokens ### Authorization Server redirect As part of the flow for the `authorization_code` grant type, the client needs to point the user to the authorization URL, so that they confirm the access request. This design proposes that it will be supported via a pluggable dependency that will initiate this process in an application-specific way: ```go type AuthorizationCodeHandler struct { ... // AuthorizationCodeFetcher is a required function called to initiate the authorization flow. // It is responsible for opening the URL in a browser for the user to start the authorization process. // It should return the authorization code and state once the Authorization Server // redirects back to the RedirectURL. AuthorizationCodeFetcher func(ctx context.Context, args *AuthorizationArgs) (*AuthorizationResult, error) ... } ``` The function is supposed perform any application specific logic to handle the redirect from the Authorization Server and return the resulting code and state. ## `oauthex` changes Some additional/adjusted building blocks that may be useful when creating `OAuthHandler` implementations are present in the `oauthex` package: - `auth_meta.go`: Authorization Server Metadata utilities: - `GetAuthServerMeta`: get Authorization Server Metadata from a URL - `dcr.go`: Dynamic Client Registration utilities (unchanged) - `resource_meta.go`: Protected Resource Metadata utilities: - `GetProtectedResourceMetadata`: get Protected Resource Metadata from a URL - `ParseWWWAuthenticate` – as per name (unchanged) - [deprecated] `GetProtectedResourceMetadataFromID` and `GetProtectedResourceMetadataFromHeader` in favor of more generic `GetProtectedResourceMetadata`. They will be kept under the Go build tag and removed one version of the SDK in the future.
105 lines
5.4 KiB
Go
105 lines
5.4 KiB
Go
// Copyright 2025 The Go MCP SDK Authors. All rights reserved.
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// Use of this source code is governed by an MIT-style
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// license that can be found in the LICENSE file.
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// This file implements Protected Resource Metadata.
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// See https://www.rfc-editor.org/rfc/rfc9728.html.
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// This is a temporary file to expose the required objects to the main package.
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package oauthex
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// ProtectedResourceMetadata is the metadata for an OAuth 2.0 protected resource,
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// as defined in section 2 of https://www.rfc-editor.org/rfc/rfc9728.html.
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//
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// The following features are not supported:
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// - additional keys (§2, last sentence)
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// - human-readable metadata (§2.1)
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// - signed metadata (§2.2)
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type ProtectedResourceMetadata struct {
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// Resource (resource) is the protected resource's resource identifier.
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// Required.
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Resource string `json:"resource"`
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// AuthorizationServers (authorization_servers) is an optional slice containing a list of
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// OAuth authorization server issuer identifiers (as defined in RFC 8414) that can be
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// used with this protected resource.
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AuthorizationServers []string `json:"authorization_servers,omitempty"`
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// JWKSURI (jwks_uri) is an optional URL of the protected resource's JSON Web Key (JWK) Set
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// document. This contains public keys belonging to the protected resource, such as
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// signing key(s) that the resource server uses to sign resource responses.
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JWKSURI string `json:"jwks_uri,omitempty"`
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// ScopesSupported (scopes_supported) is a recommended slice containing a list of scope
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// values (as defined in RFC 6749) used in authorization requests to request access
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// to this protected resource.
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ScopesSupported []string `json:"scopes_supported,omitempty"`
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// BearerMethodsSupported (bearer_methods_supported) is an optional slice containing
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// a list of the supported methods of sending an OAuth 2.0 bearer token to the
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// protected resource. Defined values are "header", "body", and "query".
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BearerMethodsSupported []string `json:"bearer_methods_supported,omitempty"`
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// ResourceSigningAlgValuesSupported (resource_signing_alg_values_supported) is an optional
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// slice of JWS signing algorithms (alg values) supported by the protected
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// resource for signing resource responses.
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ResourceSigningAlgValuesSupported []string `json:"resource_signing_alg_values_supported,omitempty"`
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// ResourceName (resource_name) is a human-readable name of the protected resource
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// intended for display to the end user. It is RECOMMENDED that this field be included.
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// This value may be internationalized.
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ResourceName string `json:"resource_name,omitempty"`
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// ResourceDocumentation (resource_documentation) is an optional URL of a page containing
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// human-readable information for developers using the protected resource.
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// This value may be internationalized.
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ResourceDocumentation string `json:"resource_documentation,omitempty"`
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// ResourcePolicyURI (resource_policy_uri) is an optional URL of a page containing
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// human-readable policy information on how a client can use the data provided.
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// This value may be internationalized.
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ResourcePolicyURI string `json:"resource_policy_uri,omitempty"`
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// ResourceTOSURI (resource_tos_uri) is an optional URL of a page containing the protected
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// resource's human-readable terms of service. This value may be internationalized.
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ResourceTOSURI string `json:"resource_tos_uri,omitempty"`
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// TLSClientCertificateBoundAccessTokens (tls_client_certificate_bound_access_tokens) is an
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// optional boolean indicating support for mutual-TLS client certificate-bound
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// access tokens (RFC 8705). Defaults to false if omitted.
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TLSClientCertificateBoundAccessTokens bool `json:"tls_client_certificate_bound_access_tokens,omitempty"`
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// AuthorizationDetailsTypesSupported (authorization_details_types_supported) is an optional
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// slice of 'type' values supported by the resource server for the
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// 'authorization_details' parameter (RFC 9396).
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AuthorizationDetailsTypesSupported []string `json:"authorization_details_types_supported,omitempty"`
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// DPOPSigningAlgValuesSupported (dpop_signing_alg_values_supported) is an optional
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// slice of JWS signing algorithms supported by the resource server for validating
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// DPoP proof JWTs (RFC 9449).
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DPOPSigningAlgValuesSupported []string `json:"dpop_signing_alg_values_supported,omitempty"`
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// DPOPBoundAccessTokensRequired (dpop_bound_access_tokens_required) is an optional boolean
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// specifying whether the protected resource always requires the use of DPoP-bound
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// access tokens (RFC 9449). Defaults to false if omitted.
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DPOPBoundAccessTokensRequired bool `json:"dpop_bound_access_tokens_required,omitempty"`
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// SignedMetadata (signed_metadata) is an optional JWT containing metadata parameters
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// about the protected resource as claims. If present, these values take precedence
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// over values conveyed in plain JSON.
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// TODO:implement.
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// Note that §2.2 says it's okay to ignore this.
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// SignedMetadata string `json:"signed_metadata,omitempty"`
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}
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// Challenge represents a single authentication challenge from a WWW-Authenticate header.
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// As per RFC 9110, Section 11.6.1, a challenge consists of a scheme and optional parameters.
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type Challenge struct {
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// Scheme is the authentication scheme (e.g., "Bearer", "Basic").
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// It is case-insensitive. A parsed value will always be lower-case.
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Scheme string
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// Params is a map of authentication parameters.
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// Keys are case-insensitive. Parsed keys are always lower-case.
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Params map[string]string
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}
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