User module | Login Feature

# User Login Process

### User Story

- Upon entering correct username and password in the login form, the system verifies the input, grants access to the user's account, and navigates to the user homepage
- When incorrect or incomplete username and password are entered in the login form, the system displays error messages and advises the user to input accurate credentials for successful login..

### Task

- [x] Implement Data Access Object (DAO) Layer.
- [x] Implement Service Layer.
- [x] Create JUnit Test Cases.
- [x] Ensure that the test cases are passing.
- [ ] Write clear and concise comments in the code to explain complex logic.

### DAO
- findUserByEmail()

### Service
- loginUser()

### Service Test
TestLoginFeature
- testLoginSuccess()
- testLoginFailure()

### Estimation
- 2 hours

# Flowchart

```mermaid
flowchart TD
A[Start]
B[Display Login Form]
C[User Provides Credentials]
D[Validate Credentials]
E{Credentials Valid?}
F[Grant Access]
G[Login Successful]
H[Display Error Messages]
I[End]

A --> B
B --> C
C --> D
D --> E
E -- Yes --> F
F --> G
E -- No --> H
H --> B
H --> I
G --> I
```