code: func IdentityFilterByProviderType(providerType string) func(db *gorm.DB) *gorm.DB {
  	return func(db *gorm.DB) *gorm.DB {
  		return db.Where("provider_type = ?", providerType)
  	}
  }
docs: // IdentityFilterByProviderType is a gorm filter by 'provider_type'