source: src/main/java/com/example/autopartz/config/CustomUsernamePasswordAuthenticationProvider.java

package com.example.autopartz.config;

import com.example.autopartz.service.UserService;
import org.springframework.security.authentication.AuthenticationProvider;
import org.springframework.security.authentication.BadCredentialsException;
import org.springframework.security.authentication.UsernamePasswordAuthenticationToken;
import org.springframework.security.core.Authentication;
import org.springframework.security.core.AuthenticationException;
import org.springframework.security.core.userdetails.UserDetails;
import org.springframework.security.crypto.password.PasswordEncoder;
import org.springframework.stereotype.Component;

import java.util.Objects;

@Component
public class CustomUsernamePasswordAuthenticationProvider implements AuthenticationProvider {

    private final UserService userService;
    private final PasswordEncoder passwordEncoder;

    public CustomUsernamePasswordAuthenticationProvider(UserService userService, PasswordEncoder passwordEncoder) {
        this.userService = userService;
        this.passwordEncoder = passwordEncoder;
    }

    @Override
    public Authentication authenticate(Authentication authentication) throws AuthenticationException {
        String username = authentication.getName();
        String password = authentication.getCredentials().toString();

        if ("".equals(username) || "".equals(password)) {
            throw new BadCredentialsException("Invalid Credentials");
        }

        UserDetails userDetails = this.userService.findByUsername(username);
        String realPassword = userDetails.getPassword();
        if (!Objects.equals(password,realPassword)) {
            throw new BadCredentialsException("Password is incorrect!");
        }
        return new UsernamePasswordAuthenticationToken(userDetails, userDetails.getPassword(), userDetails.getAuthorities());

    }

    @Override   
    public boolean supports(Class<?> aClass) {
        return aClass.equals(UsernamePasswordAuthenticationToken.class);
    }
}