According to the Warden docs, #redirect! won't take effect unless a :warden symbol is thrown.

Eoin Hennessy · Eoin Hennessy · commit e6e6d3db69ad · 2010-01-31T23:32:30.000-08:00
diff --git a/lib/warden_oauth/strategy.rb b/lib/warden_oauth/strategy.rb
@@ -44,7 +44,7 @@ def authenticate!
         if params.include?('warden_oauth_provider')
           store_request_token_on_session
           redirect!(request_token.authorize_url)
-
+          throw(:warden)
         elsif params.include?('oauth_token')
           load_request_token_from_session
           if missing_stored_token?
