Backend error log:
org.springframework.security.oauth2.core.OAuth2AuthenticationException: [invalid_user_info_response] An error occurred reading the UserInfo response: [invalid_user_info_response] An error occurred while attempting to retrieve the UserInfo Resource from 'https://{TEST_URL}.auth.eu-central-1.amazoncognito.com/oauth2/userinfo': response contains invalid content type 'text/html;charset=UTF-8'. The UserInfo Response should return a JSON object (content type 'application/json') that contains a collection of name and value pairs of the claims about the authenticated End-User. Please ensure the UserInfo Uri in UserInfoEndpoint for Client Registration 'oidc' conforms to the UserInfo Endpoint, as defined in OpenID Connect 1.0: 'https://openid.net/specs/openid-connect-core-1_0.html#UserInfo'
at org.springframework.security.oauth2.client.userinfo.DefaultReactiveOAuth2UserService.lambda$loadUser$5(DefaultReactiveOAuth2UserService.java:154)
I've changed our domain name to {TEST_URL}.