public static final void validateToken(AuthToken token) throws IllegalArgumentException {
        if (token.getExpiresOn().before(new Date())) {
            throw new IllegalArgumentException("Authentication token expired: " + token.getExpiresOn()); //$NON-NLS-1$
        }
        String validSig = generateSignature(token);
        if (token.getSignature() == null || !token.getSignature().equals(validSig)) {
            throw new IllegalArgumentException("Missing or invalid signature on the auth token."); //$NON-NLS-1$
        }
    }
Validates an auth token.  This checks the expiration time of the token against 
the current system time.  It also checks the validity of the signature.
@param token the authentication token
@throws IllegalArgumentException when the token is invalid
common/auth/src/main/java/io/apiman/common/auth/AuthTokenUtil.java