Make the failed login respond a 422

src/main/kotlin/io/realworld/exception/InvalidLoginException.kt

+package io.realworld.exception
+
+class InvalidLoginException(val field: String, val error: String) : RuntimeException()

src/main/kotlin/io/realworld/service/UserService.kt

@@ -2,12 +2,14 @@ package io.realworld.service
 
 import io.jsonwebtoken.Jwts
 import io.jsonwebtoken.SignatureAlgorithm
+import io.realworld.exception.InvalidLoginException
 import io.realworld.model.User
 import io.realworld.model.inout.Login
 import io.realworld.repository.UserRepository
 import org.mindrot.jbcrypt.BCrypt
 import org.springframework.beans.factory.annotation.Value
 import org.springframework.stereotype.Service
+import org.springframework.validation.Errors
 import java.util.*
 
 @Service
@@ -59,8 +61,9 @@ class UserService(val userRepository: UserRepository,
             if (BCrypt.checkpw(login.password!!, it.password)) {
                 return updateToken(it)
             }
+            throw InvalidLoginException("password", "invalid password")
         }
-        return null
+        throw InvalidLoginException("email", "unknown email")
     }
 
 }

src/main/kotlin/io/realworld/web/UserHandler.kt

 package io.realworld.web
 
-import io.realworld.exception.ForbiddenRequestException
-import io.realworld.exception.InvalidRequest
-import io.realworld.exception.UnauthorizedException
+import io.realworld.exception.*
 import io.realworld.jwt.ApiKeySecured
 import io.realworld.model.User
 import io.realworld.model.inout.Login
@@ -25,11 +23,16 @@ class UserHandler(val repository: UserRepository,
     fun login(@Valid @RequestBody login: Login, errors: Errors): Any {
         InvalidRequest.check(errors)
 
+        try {
             service.login(login)?.let {
                 return view(service.updateToken(it))
             }
-
-        throw ForbiddenRequestException()
+            return ForbiddenRequestException()
+        } catch (e: InvalidLoginException) {
+            val errors = org.springframework.validation.BindException(this, "")
+            errors.addError(FieldError("", e.field, e.error))
+            throw InvalidException(errors)
+        }
     }
 
     @PostMapping("/api/users")