ERROR 405 after successful login at SAML IdP

I am trying to set up Nextcloud SSO with a SAML IdP Auth0.com I have been successful for users in the Auth0 internal database, but for users from Google I get a 405 Method Not Allowed error when Auth0 makes a GET request to MY_NEXTCLOUD.com/apps/user_saml/saml/acs.

This behavior is seen on multiple browsers and multiple client OS.

I am running Nextcloud 13 Docker apache image with a nginx reverse proxy, user_saml app is at 14.2.

When the process is successful, from the browser dev tools interface and SAML tools, I can see:

  1. Client redirects to Auth0
  2. After logging in using Auth0 credentials, Auth0 POSTs SAML response to the Nextcloud ACS endpoint
  3. Login is successful and access is authorized by the Client

The process fails for multiple users:

  1. Client redirects to Auth0
  2. Select Login with Google
  3. After logging in, the browser shows a blank screen, abbreviated network flow is as follows:

This last GET results in a 405 response from Nextcloud. It seems to me that on the way out, the SAML request and authentication has been successful between Nextcloud and the SAML IdP, but Nextcloud did not have a chance to process the SAML assertion as the process broke down on the way back from the SAML IdP.

I have studied as much information as I can find but I have not been to make any progress. I would be grateful if anyone can assist or has any suggestions,

Regards, Wilson

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