Adapts an OAuthClientProvider to the minimal AuthProvider interface that
transports consume. Called once at transport construction — the transport stores
the adapted provider for _commonHeaders() and 401 handling, while keeping the
original OAuthClientProvider for OAuth-specific paths (finishAuth(), 403 upscoping).
Adapts an
OAuthClientProviderto the minimalAuthProviderinterface that transports consume. Called once at transport construction — the transport stores the adapted provider for_commonHeaders()and 401 handling, while keeping the originalOAuthClientProviderfor OAuth-specific paths (finishAuth(), 403 upscoping).