Allow custom HTTP clients for OAuth (#908)

* feat: allow custom HTTP clients for OAuth

* fix(auth): preserve configured client for refresh

* fix(auth): harden OAuth HTTP adapter

* refactor(auth): simplify OAuth HTTP plumbing

* fix(auth): stop refresh token redirects by default

* fix(auth): re-export OAuth HTTP client types

Author: jif-oai

crates/rmcp/src/transport.rs

@@ -101,8 +101,9 @@ pub use auth::JwtSigningAlgorithm;
 pub use auth::{
     AuthClient, AuthError, AuthorizationManager, AuthorizationSession, AuthorizedHttpClient,
     ClientCredentialsConfig, CredentialStore, EXTENSION_OAUTH_CLIENT_CREDENTIALS,
-    InMemoryCredentialStore, InMemoryStateStore, ScopeUpgradeConfig, StateStore,
-    StoredAuthorizationState, StoredCredentials, WWWAuthenticateParams,
+    InMemoryCredentialStore, InMemoryStateStore, OAuthHttpClient, OAuthHttpClientError,
+    OAuthHttpClientFuture, OAuthHttpRedirectPolicy, OAuthHttpRequest, ScopeUpgradeConfig,
+    StateStore, StoredAuthorizationState, StoredCredentials, WWWAuthenticateParams,
 };
 
 // #[cfg(feature = "transport-ws")]