Sometime during the second half of June 2017 our integration to a Salseforce community stopped working correctly. When we try and login, the oauth flow starts and when we try and get to the salesforce login page, we can’t get the login form to display. It just takes us to a blank page at:
/setup/secur/RemoteAccessAuthorizationPage.apexp
If I login to salesforce prior, and try and start the flow, I successfully login to auth0.
From a quick online search you’re redirected to the expected URL as RemoteAccessAuthorizationPage.apexp would be the page used when Salesforce needs to authenticate/authorize the user before allowing the application to receive the user identity.
Ensure that you did not performed any configuration changes from the Salesforce side, for example, if Salesforce allows the customization of that login page check if there were any changes made that could cause this and/or try to reset any customization to the default. You may also consider reaching to Salesforce support as the issue may be on their side.