We implemented OAuth 2.0 using Web Server Authentication Flow. It was working fine in October/November but all of a sudden it has stopped working. Whenever we try authorising another client the server return (400) Bad Request with the body
{"error":"unsupported_grant_type","error_description":"grant type not supported"}
grant_type is set as authorization_code which is definitely valid.
Is there any reason why OAuth would suddenly stop working?
This is how we have implemented OAuth:
First user is directed to: https://login.salesforce.com/services/oauth2/authorize?response_type=code&client_id=blah.id&redirect_uri=https://domain.com/Web/Salesforce/Callback.aspx&scope=api%20refresh_token
User is prompted by Salesforce to login to their account.
Once user is authenticated Salesforce calls Callback.aspx, Callback.aspx requests refresh token on behalf of the client by making a POST request to: https://login.salesforce.com/services/oauth2/token with the payload:
grant_type=authorization_code&code=blah.code&client_id=blah.Id&client_secret=11111111&redirect_uri=https://domain.com/Web/Salesforce/Callback.aspx
Content type is definitely: application/x-www-form-urlencoded