public final Number expirationTime() throws OAuthBearerIllegalTokenException {
        return claim("exp", Number.class);
    }
Return the
<a href="https://tools.ietf.org/html/rfc7519#section-4.1.4">Expiration
Time</a> claim

@return the <a href=
        "https://tools.ietf.org/html/rfc7519#section-4.1.4">Expiration
        Time</a> claim if available, otherwise null
@throws OAuthBearerIllegalTokenException
            if the claim value is the incorrect type
clients/src/main/java/org/apache/kafka/common/security/oauthbearer/internals/unsecured/OAuthBearerUnsecuredJws.java