[MM-28125] einterface/oauthprovide: return parsing errors (#15426)

* einterface/oauthprovide: return parsing errors

* Update app/oauth.go

* reflect review comments

* fix var name error

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

app/user.go

@@ -328,10 +328,9 @@ func (a *App) CreateOAuthUser(service string, userData io.Reader, teamId string)
 	if provider == nil {
 		return nil, model.NewAppError("CreateOAuthUser", "api.user.create_oauth_user.not_available.app_error", map[string]interface{}{"Service": strings.Title(service)}, "", http.StatusNotImplemented)
 	}
-	user := provider.GetUserFromJson(userData)
-
-	if user == nil {
-		return nil, model.NewAppError("CreateOAuthUser", "api.user.create_oauth_user.create.app_error", map[string]interface{}{"Service": service}, "", http.StatusInternalServerError)
+	user, err1 := provider.GetUserFromJson(userData)
+	if err1 != nil {
+		return nil, model.NewAppError("CreateOAuthUser", "api.user.create_oauth_user.create.app_error", map[string]interface{}{"Service": service}, err1.Error(), http.StatusInternalServerError)
 	}
 
 	suchan := make(chan store.StoreResult, 1)
@@ -1857,9 +1856,9 @@ func (a *App) AutocompleteUsersInTeam(teamId string, term string, options *model
 }
 
 func (a *App) UpdateOAuthUserAttrs(userData io.Reader, user *model.User, provider einterfaces.OauthProvider, service string) *model.AppError {
-	oauthUser := provider.GetUserFromJson(userData)
-	if oauthUser == nil {
-		return model.NewAppError("UpdateOAuthUserAttrs", "api.user.update_oauth_user_attrs.get_user.app_error", map[string]interface{}{"Service": service}, "", http.StatusBadRequest)
+	oauthUser, err1 := provider.GetUserFromJson(userData)
+	if err1 != nil {
+		return model.NewAppError("UpdateOAuthUserAttrs", "api.user.update_oauth_user_attrs.get_user.app_error", map[string]interface{}{"Service": service}, err1.Error(), http.StatusBadRequest)
 	}
 
 	userAttrsChanged := false