private String principalLogText() {
        return expiringCredential == null ? principalName
                : expiringCredential.getClass().getSimpleName() + ":" + principalName;
    }
Determine when to sleep until before performing a refresh

@param relativeToMs
           the point (in terms of number of milliseconds since the epoch) at
           which to perform the calculation
@return null if no refresh should occur, otherwise the time to sleep until
        (in terms of the number of milliseconds since the epoch) before
        performing a refresh
clients/src/main/java/org/apache/kafka/common/security/oauthbearer/internals/expiring/ExpiringCredentialRefreshingLogin.java