we are using the implicit flow together with a Single Page Application in Okta and can retrieve the access token from the frontend using okta-auth-js, but we are not able to retrieve the user information in the (Java) backend using the token the following way:
UserInfoTokenServices tokenServices = new UserInfoTokenServices("https://dev****.oktapreview.com/oauth2/default/v1/userinfo", resource.getClientId());
With this we got an invalid_token exception. Unfortunately the user information retrieval even failed using postman.
We double checked the token using https://jwt.io/ and it was proper.
Can you give us more insights what we are missing?