KGirman

Нашел решение

WebSecurityConfig.java

package com.todo.todo.config;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Configuration;
import org.springframework.security.config.annotation.authentication.builders.AuthenticationManagerBuilder;
import org.springframework.security.config.annotation.web.builders.HttpSecurity;
import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;
import org.springframework.security.config.annotation.web.configuration.WebSecurityConfigurerAdapter;
import org.springframework.security.crypto.bcrypt.BCryptPasswordEncoder;
import com.todo.todo.services.UserService;

@Configuration
@EnableWebSecurity
public class WebSecurityConfig extends WebSecurityConfigurerAdapter {

	@Autowired
	private UserService userService;

	@Override
    protected void configure(HttpSecurity http) throws Exception {
        http
			.authorizeHttpRequests((requests) -> requests
				.antMatchers("/",
				"/index",
				"/tasks",
				"/users",
				"/registrate",
				"/logout",
				"/deleteuser/**",
				"/create",
				"/delete/**",
				"/update/**",
				"/create_task",
				"/update_task",
				"/h2-console/**",
				"/webjars/**").permitAll()
				.anyRequest().authenticated()
			)
			.formLogin((form) -> form
				.loginPage("/login")
				.permitAll()
			)
			.logout((logout) -> logout.permitAll());
    }
    @Override
    protected void configure(AuthenticationManagerBuilder auth) throws Exception {
    auth
		.userDetailsService(userService)
		.passwordEncoder(new BCryptPasswordEncoder());
    }
}

UserController.java
Добавил кодирование пароля в @PostMapping("/registrate")

// some imports here
import org.springframework.security.crypto.bcrypt.BCryptPasswordEncoder;

// some methods here

@PostMapping("/registrate")
    public String registrateUser(@Valid User user, Map<String, Object> map){
        User userFromDatabase = userRepository.findByUsername(user.getUsername());
        if(userFromDatabase != null){
            map.put("message", "User has been already registrated!");
            return registratePage;
        }
        String encodedPassword = new BCryptPasswordEncoder().encode(user.getPassword());
        user.setPassword(encodedPassword);
        user.setCreatedDate(Instant.now());
        user.setRoles(Collections.singleton(Role.USER));
        userRepository.save(user);
        map.put("message", "User has been successfully registrated!");
        return redirectLoginPage;
    }