public String subject() throws OAuthBearerIllegalTokenException {
        return claim("sub", String.class);
    }
Return the
<a href="https://tools.ietf.org/html/rfc7519#section-4.1.2">Subject</a> claim

@return the <a href=
        "https://tools.ietf.org/html/rfc7519#section-4.1.2">Subject</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