Added logic to findByEmail and login methods

src/main/java/mate/academy/service/AuthenticationService.java

@@ -1,5 +1,7 @@
 package mate.academy.service;
 
+import mate.academy.model.User;
+
 public class AuthenticationService {
     /**
      * Imagine that some user wants to login to your site.
@@ -10,7 +12,12 @@ public class AuthenticationService {
      * @return true if user by email exists and passed password is equal to user's password.
      * Return false in any other cases.
      */
+    private final UserService userService = new UserService();
     public boolean login(String email, String password) {
+        User user = userService.findByEmail(email);
+        if (user != null && password.equals(user.getPassword())){
+            return true;
+        }
         return false;
     }
 }

src/main/java/mate/academy/service/UserService.java

@@ -15,6 +15,11 @@ public class UserService {
      * Return <code>null</code> if there is no suitable user
      */
     public User findByEmail(String email) {
+    for(User user : users){
+        if(user.getEmail().equals(email)){
+            return user;
+        }
+    }
         return null;
     }
 }