Use Keycloak for OIDC authentication

Select/create a Realm and Client. Select a Client and visit Settings.
Client Protocol: openid-connect
Access Type: confidential
Standard Flow Enabled: On
Configure Root URL such as http://vault.example.com
Configure Valid Redirect URIs such as
- http://vault.example.com/ui/vault/auth/oidc/oidc/callback
- http://vault.example.com/oidc/oidc/callback
Save.
Visit Credentials. Select Client ID and Secret and note the generated secret.