final MSAAuthenticator msa = new MSAAuthenticator("CLIENT_ID", 5678);

final MinecraftProfile profile = msa.login("[email protected]", "youshallnotpass11");

final String url = msa.browser((accessToken) -> {
  // You can do what you want with the access token, but we're going to login with it for example
  final MinecraftProfile profile = msa.login(accessToken);
  if (profile != null)
  {
    // Handle here
  }
});
// For example, we'll browse to this URL
Desktop.getDesktop().browse(new URI(url)); 

// Or say you have a refresh token because your access token expired.
final String accessToken = msa.refresh(refreshToken);
final MinecraftProfile profile = msa.login(accessToken);