GoogleAuth is a Java server library that implements the Time-based One-time Password (TOTP) algorithm specified in RFC 6238.

This implementation borrows from Google Authenticator, whose C code has served as a reference, and was created upon code published in this blog post by Enrico M. Crisostomo.

Any developer who wants to add TOTP multi-factor authentication to a Java application and needs the server-side code to create TOTP shared secrets, generate and verify TOTP passwords.

Users may use TOTP-compliant token devices (such as those you get from your bank), or a software-based token application (such as Google Authenticator).

The minimum Java version required to build and use this library is Java 7.

Add a dependency to your build environment.

If you are using Maven:

<dependency>
  <groupId>com.warrenstrange</groupId>
  <artifactId>googleauth</artifactId>
  <version>1.4.0</version>
</dependency>

If you are using Gradle:

 compile 'com.warrenstrange:googleauth:1.4.0'

The required libraries will be automatically pulled into your project:

• Apache Commons Codec.
• Apache HTTP client.

Both the Google Authenticator client applications (available for iOS, Android and BlackBerry) and its PAM module can be used to generate codes to be validated by this library.

However, this library can also be used to build custom client applications if Google Authenticator is not available on your platform or if it cannot be used.

This library includes full JavaDoc documentation and a JUnit test suite that can be used as example code for most of the library purposes.

Texinfo documentation sources are also included and a PDF manual can be generated by an Autotools-generated Makefile:

• To bootstrap the Autotools, the included autogen.sh script can be used.

  $ ./autogen.sh
  

• Configure and build the documentation:

  $ ./configure
  $ make pdf
  

Since typical users will not have a TeX distribution installed in their computers, the PDF manuals for every version of GoogleAuth are hosted at this address.

The following code creates a new set of credentials for a user. No user name is provided to the API and it is a responsibility of the caller to save it for later use during the authorisation phase.

GoogleAuthenticator gAuth = new GoogleAuthenticator();
final GoogleAuthenticatorKey key = gAuth.createCredentials();

The user should be given the value of the shared secret, returned by

key.getKey()

so that the new account can be configured into its token device. A convenience method is provided to easily encode the secret key and the account information into a QRcode.

When a user wishes to log in, he will provide the TOTP password generated by his device. By default, a TOTP password is a 6 digit integer that changes every 30 seconds. Both the password length and its validity can be changed. However, many token devices such as Google Authenticator use the default values specified by the TOTP standard and they do not allow for any customization.

The following code checks the validity of the specified password against the provided Base32-encoded secretKey:

GoogleAuthenticator gAuth = new GoogleAuthenticator();
boolean isCodeValid = gAuth.authorize(secretKey, password);

Since TOTP passwords are time-based, it is essential that the clock of both the server and the client are synchronised within the tolerance used by the library. The tolerance is set by default to a window of size 3 and can be overridden when configuring a GoogleAuthenticator instance.

This library can generate TOTP codes for testing or for use as a software-based client.

GoogleAuthenticator gAuth = new GoogleAuthenticator();
int code = gAuth.getTotpPassword(secretKey);

The codes generated in this way can be used as an alternative to the codes that would be generated by the Google Authenticator App (or other client device).

By default 5 scratch codes are generated together with a new shared secret. Scratch codes are meant to be a safety net in case a user loses access to their token device. Scratch nodes are not a functionality required by the TOTP standard and it is up to the developer to decide whether they should be used in his application.

The library can assist with fetching and storing user credentials and a hook is provided to users who want to integrate this functionality. The ICredentialRepository interface defines the contract between a credential repository and this library.

The credential repository can be set in multiple ways:

• The credential repository can be set on a per-instance basis, using the credentialRepository property of the IGoogleAuthenticator interface.

• The library looks for instances of this interface using the Java ServiceLoader API (introduced in Java 6), that is, scanning the META-INF/services package looking for a file named com.warrenstrange.googleauth.ICredentialRepository and, if found, loading the provider classes listed therein.

Two methods needs to be implemented in the ICredentialRepository interface.

• String getSecretKey(String userName).
• void saveUserCredentials(String userName, ...).

The credentials repository establishes the relationship between a user name and its credentials. This way, API methods receiving only a user name instead of credentials can be used.

The following code creates a new set of credentials for the user Bob and stores them on the configured ICredentialRepository instance:

GoogleAuthenticator gAuth = new GoogleAuthenticator();
final GoogleAuthenticatorKey key = gAuth.createCredentials("Bob");

The following code checks the validity of the specified code against the secret key of the user Bob returned by the configured ICredentialRepository instance:

GoogleAuthenticator gAuth = new GoogleAuthenticator();
boolean isCodeValid = gAuth.authorizeUser("Bob", code);

If an attempt is made to use such methods when no credential repository is configured, an exception is thrown:

java.lang.UnsupportedOperationException: An instance of the
  com.warrenstrange.googleauth.ICredentialRepository service must be
  configured in order to use this feature.

Please, read the manual before opening a ticket. If you have read the manual and you still think the behaviour you are observing is a bug, then open a ticket on github.

Copyright (c) 2013 Warren Strange

Copyright (c) 2014-2019 Enrico M. Crisostomo

All rights reserved.

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