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Merged
aheritier merged 1 commit into from
Aug 14, 2026
+437 −46
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refactor(mcp): share protected resource metadata discovery #3955

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113 changes: 69 additions & 44 deletions pkg/tools/mcp/oauth.go
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Original file line number Diff line number Diff line change
Expand Up @@ -268,6 +268,73 @@ func resourceMetadataFromWWWAuth(wwwAuth string) string {
return params["resource"]
}

// protectedResourceMetadataOptions configures fetchProtectedResourceMetadata.
type protectedResourceMetadataOptions struct {
// FallbackCandidateURLs are additional protected-resource metadata URLs
// tried, in order, only after the primary resourceURL 404s. Leave this
// empty for runtime callers, which must preserve the existing
// single-candidate, supplied-origin-default behavior exactly. Computing
// these candidates (RFC 9728 path-insertion, then origin-root) is the
// standalone CLI discovery flow's responsibility, not this helper's.
FallbackCandidateURLs []string
}

// fetchProtectedResourceMetadata fetches and decodes RFC 9728 OAuth
// protected-resource metadata for a challenged MCP server, deduplicating
// logic shared by the runtime-managed and docker-agent-driven unmanaged
// OAuth flows.
//
// resourceURL is the primary candidate (normally the challenge's
// resource_metadata, or otherwise authServer's
// /.well-known/oauth-protected-resource). A 404 on a candidate is not an
// error: it is treated as an empty metadata document, matching current
// runtime behavior, and AuthorizationServers is defaulted to authServer
// below once every candidate has been tried.
//
// Any decode failure or non-404/non-200 response (including another 2xx
// like 201 or 204) on any attempted candidate is a hard error: no further
// candidate is tried and the caller must not proceed to authorization-server
// discovery, DCR, or token work.
func fetchProtectedResourceMetadata(ctx context.Context, client *http.Client, resourceURL, authServer string, opts protectedResourceMetadataOptions) (protectedResourceMetadata, error) {
candidates := append([]string{resourceURL}, opts.FallbackCandidateURLs...)

var metadata protectedResourceMetadata
for _, candidateURL := range candidates {
req, err := http.NewRequestWithContext(ctx, http.MethodGet, candidateURL, http.NoBody)
if err != nil {
return protectedResourceMetadata{}, err
}
resp, err := client.Do(req)
if err != nil {
return protectedResourceMetadata{}, err
}

if resp.StatusCode == http.StatusNotFound {
resp.Body.Close()
continue
}
if resp.StatusCode != http.StatusOK {
_, _ = io.ReadAll(resp.Body)
resp.Body.Close()
return protectedResourceMetadata{}, errors.New("failed to fetch protected resource metadata")
}

decodeErr := json.NewDecoder(resp.Body).Decode(&metadata)
resp.Body.Close()
if decodeErr != nil {
return protectedResourceMetadata{}, decodeErr
}
break
}

if len(metadata.AuthorizationServers) == 0 {
slog.DebugContext(ctx, "No authorization servers in resource metadata, using auth server from WWW-Authenticate header")
metadata.AuthorizationServers = []string{authServer}
}

return metadata, nil
}

// parseAuthParams parses the top-level auth-params across every challenge
// in a WWW-Authenticate header value (RFC 7235 auth-param, as profiled by
// RFC 6750 for the Bearer scheme) into a single lowercase-key map. It is
Expand Down Expand Up @@ -1148,31 +1215,10 @@ func (t *oauthTransport) handleManagedOAuthFlow(ctx context.Context, authServer,
resourceURL := cmp.Or(resourceMetadataFromWWWAuth(wwwAuth), authServer+"/.well-known/oauth-protected-resource")

span.AddEvent("oauth.step", trace.WithAttributes(attribute.String("cagent.oauth.step", "fetch_protected_resource_metadata")))
resourceReq, err := http.NewRequestWithContext(ctx, http.MethodGet, resourceURL, http.NoBody)
resourceMetadata, err := fetchProtectedResourceMetadata(ctx, t.oauthClient(), resourceURL, authServer, protectedResourceMetadataOptions{})
if err != nil {
return err
}
resp, err := t.oauthClient().Do(resourceReq)
if err != nil {
return err
}
defer resp.Body.Close()

if resp.StatusCode != http.StatusOK && resp.StatusCode != http.StatusNotFound {
_, _ = io.ReadAll(resp.Body)
return errors.New("failed to fetch protected resource metadata")
}
var resourceMetadata protectedResourceMetadata
if resp.StatusCode == http.StatusOK {
if err := json.NewDecoder(resp.Body).Decode(&resourceMetadata); err != nil {
return err
}
}

if len(resourceMetadata.AuthorizationServers) == 0 {
slog.DebugContext(ctx, "No authorization servers in resource metadata, using auth server from WWW-Authenticate header")
resourceMetadata.AuthorizationServers = []string{authServer}
}

oauth := &oauth{metadataClient: t.oauthClient()}
span.AddEvent("oauth.step", trace.WithAttributes(attribute.String("cagent.oauth.step", "fetch_authorization_server_metadata")))
Expand Down Expand Up @@ -1438,31 +1484,10 @@ func (t *oauthTransport) handleUnmanagedOAuthFlow(ctx context.Context, authServe
resourceURL := cmp.Or(resourceMetadataFromWWWAuth(wwwAuth), authServer+"/.well-known/oauth-protected-resource")

span.AddEvent("oauth.step", trace.WithAttributes(attribute.String("cagent.oauth.step", "fetch_protected_resource_metadata")))
resourceReq, err := http.NewRequestWithContext(ctx, http.MethodGet, resourceURL, http.NoBody)
resourceMetadata, err := fetchProtectedResourceMetadata(ctx, t.oauthClient(), resourceURL, authServer, protectedResourceMetadataOptions{})
if err != nil {
return err
}
resp, err := t.oauthClient().Do(resourceReq)
if err != nil {
return err
}
defer resp.Body.Close()

if resp.StatusCode != http.StatusOK && resp.StatusCode != http.StatusNotFound {
_, _ = io.ReadAll(resp.Body)
return errors.New("failed to fetch protected resource metadata")
}
var resourceMetadata protectedResourceMetadata
if resp.StatusCode == http.StatusOK {
if err := json.NewDecoder(resp.Body).Decode(&resourceMetadata); err != nil {
return err
}
}

if len(resourceMetadata.AuthorizationServers) == 0 {
slog.DebugContext(ctx, "No authorization servers in resource metadata, using auth server from WWW-Authenticate header")
resourceMetadata.AuthorizationServers = []string{authServer}
}

oauth := &oauth{metadataClient: t.oauthClient()}
span.AddEvent("oauth.step", trace.WithAttributes(attribute.String("cagent.oauth.step", "fetch_authorization_server_metadata")))
Expand Down
7 changes: 5 additions & 2 deletions pkg/tools/mcp/oauthflow/types.go
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Original file line number Diff line number Diff line change
Expand Up @@ -15,8 +15,11 @@ type OAuthToken struct {
ClientSecret string `json:"client_secret,omitempty"`
AuthServer string `json:"auth_server,omitempty"`

// RequestedScopes records the scope list the config asked for when this
// token was obtained. Unlike Scope (which is whatever the authorization
// RequestedScopes records the scope list actually requested when this
// token was obtained: the configured scopes, or — on a successful
// dynamic client registration with no configured override — the
// challenge- or protected-resource-metadata-derived scopes selected by
// selectDCRScopes. Unlike Scope (which is whatever the authorization
// server chose to return, sometimes empty, sometimes comma/space
// separated), RequestedScopes reflects our intent and is used to detect
// when the config has changed and a new OAuth flow is required.
Expand Down
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