For OIDC, there's no option to logout from IDP

[vaibhavjainv]

Describe the Bug: Hello. I am using AWS Cognito user pools to authenticate into GoAlert, which is working fine. I am using OpenID Connect Authentication (OIDC) for this. The issue is that, after user logs out from GoAlert, the user is still logged in to AWS Cognito user pool, which is why, they do not need to provide their credentials again. This is happening, because there's no way to specify a logout url that can be invoked for IDP (Cognito) when the user logs out from GoAlert.

Steps to Reproduce:

1. Set up OIDC with Cognito
2. Login using Cognito credentials
3. Logout from GoAlert
4. Try to login again

Expected Behavior: The user should be presented with login page.

Observed Behavior: The user is directly logged.