Method 'GET' not supported using SAML app

Hi. I have a SAML application configured in Zitadel. When I attempt to login to the app using SSO, I am correctly redirected to Zitadel for entering my credentials. However, I am not successfully redirected back to the app. Instead I get "Method Not Allowed", "Method 'GET' is not supported." If I am already logged into Zitadel when I attempt to login to the app using SSO, the app successfully loads. I have tried configuring a second SAML application in Zitadel and I am getting the same behavior. I must note that these are commercial apps (i.e. not created by me). Any idea as to what is causing the Method not allowed and why does it work if already logged into Zitadel?

Ask Inkeep•12/10/25, 5:45 PM

Hi @Pam Pozzi, I'm an AI assistant for ZITADEL. While a team member reviews this question, I'll see if I can find relevant sources for your question.

Ask Inkeep•12/10/25, 5:46 PM

Answer

The "Method 'GET' is not supported" error you're seeing is likely related to a known issue with the new Login UI and SAML POST binding. (1)

There is an open bug where, when "Use new Login UI" is enabled for a SAML application, POST-initiated AuthnRequests complete authentication successfully but then redirect to the ACS URL using an HTTP GET instead of the expected HTTP POST containing the SAMLResponseSAMLResponse and RelayStateRelayState.

This explains why it works when you're already logged in—in that case, the flow may bypass the problematic redirect behavior.

Potential workarounds:

Disable the new Login UI for your SAML application in the ZITADEL Console (uncheck "Use new Login UI") . This has been confirmed to work with both bindings.
Check if your SP can use HTTP-Redirect binding instead of HTTP-POST for initiating the AuthnRequest—HTTP-Redirect initiated requests reportedly work correctly even with the new Login UI enabled.

If you're self-hosting, you might also want to check your ZITADEL version, as this issue was reported on ZITADEL Cloud version 4.2.2.

Would you like me to provide a general answer with additional troubleshooting steps, or would you prefer to click the "Ask for help" button to have a team member review this?

Ask Inkeep•12/10/25, 5:46 PM

To learn more, see the sources I considered:

[1] [Bug]: SAML IdP: With Use new Login UI enabled, POST-initiated AuthnRequest redirects to ACS without SAMLResponse/RelayState

Ask Inkeep•12/10/25, 5:46 PM

Feel free to tag @Ask Inkeep with additional questions.

AAsk Inkeep To learn more, see the sources I considered: [[1] [Bug]: SAML IdP: With Use n...

Ask InkeepAPP•12/10/25, 5:48 PM

Got it. Tagging @Rajat for additional help.