Spring security switch to Ldap authentication and database authorities

You need to create a CustomAuthenticationProvider wich implements AuthenticationProvider, and override authenticate method, for example:

@Component
public class CustomAuthenticationProvider
    implements AuthenticationProvider {

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

        boolean authenticated = false;
        /**
         * Here implements the LDAP authentication
         * and return authenticated for example
         */
        if (authenticated) {

            String usernameInDB = "";
            /**
             * Here look for username in your database!
             * 
             */
            List<GrantedAuthority> grantedAuths = new ArrayList<>();
            grantedAuths.add(new     SimpleGrantedAuthority("ROLE_USER"));
            Authentication auth = new     UsernamePasswordAuthenticationToken(usernameInDB, password,     grantedAuths);
            return auth;
        } else {
            return null;
        }
    }

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

}

Then, in your SecurityConfig, you need to override the configure thats use AuthenticationManagerBuilder:

@Override
public void configure(AuthenticationManagerBuilder auth) throws Exception {
    auth.authenticationProvider(this.authenticationProvider);
}

You can autowire the CustomAuthenticationProvider doing this:

@Autowired
private CustomAuthenticationProvider authenticationProvider;

Doing this, you can override the default authentication behaviour.

Spring Security already supports LDAP out-of-the-box. It actually has a whole chapter on this.

To use and configure LDAP add the spring-security-ldap dependency and next use the AuthenticationManagerBuilder.ldapAuthentication to configure it. The LdapAuthenticationProviderConfigurer allows you to set the needed things up.

@Autowired
public void configureGlobal(AuthenticationManagerBuilder auth) throws Exception {
    auth.ldapAuthentication()
      .contextSource()
        .url(...)
        .port(...)
        .managerDn(...)
        .managerPassword(...)
      .and()
        .passwordEncoder(passwordEncoder())
        .userSearchBase(...)        
        .ldapAuthoritiesPopulator(new UserServiceLdapAuthoritiesPopulater(this.userService));      
}

Something like that (it should give you at least an idea on what/how to configure things) there are more options but check the javadocs for that. If you cannot use the UserService as is to retrieve the roles (because only the roles are in the database) then implement your own LdapAuthoritiesPopulator for that.