On the website https://code.google.com/apis/console I have registered my application, set up generated Client ID: and Client Secret to my app and tried to log in with Google. Unfortunately, I got the error message:
Error: redirect_uri_mismatch
The redirect URI in the request: http://127.0.0.1:3000/auth/google_oauth2/callback did not match a registered redirect URI
scope=https://www.googleapis.com/auth/userinfo.profile https://www.googleapis.com/auth/userinfo.email
response_type=code
redirect_uri=http://127.0.0.1:3000/auth/google_oauth2/callback
access_type=offline
approval_prompt=force
client_id=generated_id
What does mean this message, and how can I fix it? I use the gem omniauth-google-oauth2.
The redirect URI (where the response is returned to) has to be registered in the APIs console, and the error is indicating that you haven't done that, or haven't done it correctly.
Go to the console for your project and look under API Access. You should see your client ID & client secret there, along with a list of redirect URIs. If the URI you want isn't listed, click edit settings and add the URI to the list.
EDIT: (From a highly rated comment below) Note that updating the google api console and that change being present can take some time. Generally only a few minutes but sometimes it seems longer.