Update jwt regexp to include = (#16521)

Fixes #16501

pkg/login/social/generic_oauth.go

@@ -231,7 +231,7 @@ func (s *SocialGenericOAuth) extractToken(data *UserInfoJson, token *oauth2.Toke
 		return false
 	}
 
-	jwtRegexp := regexp.MustCompile("^([-_a-zA-Z0-9]+)[.]([-_a-zA-Z0-9]+)[.]([-_a-zA-Z0-9]+)$")
+	jwtRegexp := regexp.MustCompile("^([-_a-zA-Z0-9=]+)[.]([-_a-zA-Z0-9=]+)[.]([-_a-zA-Z0-9=]+)$")
 	matched := jwtRegexp.FindStringSubmatch(idToken.(string))
 	if matched == nil {
 		s.log.Debug("id_token is not in JWT format", "id_token", idToken.(string))