Simplify oauth (#8972)

* Remove unused OauthProvider::GetIdentifier

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>

* Reuse gitlab's getAuthData() instead of open-coding it

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>

* Remove OauthProvider::GetAuthDataFromJson interface

The data is already available via GetUserFromJson().AuthData

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>

api4/oauth_test.go

@@ -1127,15 +1127,8 @@ func closeBody(r *http.Response) {
 type MattermostTestProvider struct {
 }
 
-func (m *MattermostTestProvider) GetIdentifier() string {
-	return model.SERVICE_GITLAB
-}
-
 func (m *MattermostTestProvider) GetUserFromJson(data io.Reader) *model.User {
-	return model.UserFromJson(data)
-}
-
-func (m *MattermostTestProvider) GetAuthDataFromJson(data io.Reader) string {
-	authData := model.UserFromJson(data)
-	return authData.Email
+	user := model.UserFromJson(data)
+	user.AuthData = &user.Email
+	return user
 }