server/src/main/java/com/orientechnologies/orient/server/security/authenticator/ODefaultPasswordAuthenticator.java
public String authenticate(final String username, final String password) {
    String principal = null;

    try {
      OServerUserConfiguration user = getUser(username);

      if (isPasswordValid(user)) {
        if (OSecurityManager.instance().checkPassword(password, user.password)) {
          principal = user.name;
        }
      }
    } catch (Exception ex) {
      OLogManager.instance().error(this, "ODefaultPasswordAuthenticator.authenticate()", ex);
    }

    return principal;
  }
public String authenticate(final String username, final String password) {
    String principal = null;

    try {
      OServerUserConfiguration user = getUser(username);

      if (isPasswordValid(user)) {
        if (OSecurityManager.instance().checkPassword(password, user.password)) {
          principal = user.name;
        }
      }
    } catch (Exception ex) {
      OLogManager.instance().error(this, "ODefaultPasswordAuthenticator.authenticate()", ex);
    }

    return principal;
  }
Returns the actual username if successful, null otherwise.