private void handleCallback(OAuthBearerValidatorCallback callback) {
        String tokenValue = callback.tokenValue();
        if (tokenValue == null)
            throw new IllegalArgumentException("Callback missing required token value");
        String principalClaimName = principalClaimName();
        String scopeClaimName = scopeClaimName();
        List<String> requiredScope = requiredScope();
        int allowableClockSkewMs = allowableClockSkewMs();
        OAuthBearerUnsecuredJws unsecuredJwt = new OAuthBearerUnsecuredJws(tokenValue, principalClaimName,
                scopeClaimName);
        long now = time.milliseconds();
        OAuthBearerValidationUtils
                .validateClaimForExistenceAndType(unsecuredJwt, true, principalClaimName, String.class)
                .throwExceptionIfFailed();
        OAuthBearerValidationUtils.validateIssuedAt(unsecuredJwt, false, now, allowableClockSkewMs)
                .throwExceptionIfFailed();
        OAuthBearerValidationUtils.validateExpirationTime(unsecuredJwt, now, allowableClockSkewMs)
                .throwExceptionIfFailed();
        OAuthBearerValidationUtils.validateTimeConsistency(unsecuredJwt).throwExceptionIfFailed();
        OAuthBearerValidationUtils.validateScope(unsecuredJwt, requiredScope).throwExceptionIfFailed();
        log.info("Successfully validated token with principal {}: {}", unsecuredJwt.principalName(),
                unsecuredJwt.claims());
        callback.token(unsecuredJwt);
    }
Return true if this instance has been configured, otherwise false

@return true if this instance has been configured, otherwise false
clients/src/main/java/org/apache/kafka/common/security/oauthbearer/internals/unsecured/OAuthBearerUnsecuredValidatorCallbackHandler.java