Resolve "Check Email Service in production"

Related to #395 (closed)

src/main/java/at/ac/uibk/gitsearch/repository/jpa/AuthorityRepository.java

 package at.ac.uibk.gitsearch.repository.jpa;
 
 import at.ac.uibk.gitsearch.domain.Authority;
+import at.ac.uibk.gitsearch.domain.User;
 import java.util.List;
 import org.springframework.data.jpa.repository.JpaRepository;
 import org.springframework.data.jpa.repository.Modifying;
 import org.springframework.data.jpa.repository.Query;
+import org.springframework.data.repository.query.Param;
 
 /**
  * Spring Data JPA repository for the {@link Authority} entity.
@@ -22,4 +24,7 @@ public interface AuthorityRepository extends JpaRepository<Authority, String> {
     List<Authority> getUsedAuthorities();
 
     List<Authority> findAll();
+
+    @Query("SELECT u FROM User u JOIN u.authorities auth WHERE auth.name = :authority")
+    List<User> findAllUsersWithAuthority(@Param("authority") String authority);
 }