def METHOD_NAME(self, paramAsJsonNode, context):
    print "Fido2Extension. authenticateAssertionStart"
    assertionService = CdiUtil.bean(AssertionService)
    if paramAsJsonNode.hasNonNull("username"):
        print "Fido2Extension. Username: '%s'" % paramAsJsonNode.get("username").asText()
        if paramAsJsonNode.get("username").asText() == 'test_user':
            self.throwBadRequestException("Fido2Extension authenticateAssertionStart : test_user", "Description Error from script : test_user", context)
    else:
        self.throwBadRequestException("Fido2Extension authenticateAssertionStart. Username is missing.", "Description Error from script. Username is missing.", context)
    return True