module.exports = function(config) {

  authentication = function (username, password, success, fail) {
    
    if (config) {
      const crypto = require('crypto');
      if (config.passwords && config.passwords[username]) {
        if (crypto.getHashes().indexOf(config.passwords[username][0])>=0) {
          if (crypto.createHash(config.passwords[username][0]).update(password, 'utf8').digest('hex') === config.passwords[username][1]) {
            success();
            return;
          } else {
            fail();
            return;
          }
        } else {
          console.log("**** HASH NOT FOUND ****");
          console.log(config.passwords[username][0]);
          console.log(crypto.getHashes());
          fail();
          return;
        }
      }
      if (config.ldap) try {
        var LdapAuth = require('ldapauth');
        var auth = new LdapAuth(config.ldap);
        auth.authenticate(username, password, function(err, usr) {
          auth.close(function(err) {})
          if (err) {
            console.log("**** ERROR: LDAP Authentication failed:", err);
            fail();
            return;
          }
          console.log("**** SUCCESS: LDAP Authentication:");
          success();
          return;
        });
        return; // need to block here!
      } catch (e) {
        console.log("**** Error: LDAP failed: ", e, e.stack);
        fail();
        return;
      }
    }
    fail();
    return;
  }

  return authentication;

}