protected void validateIssuerClaim(final JWTClaimsSet claims, final Optional<OAuthRegisteredService> service) throws Throwable {
        LOGGER.debug("Validating claims as [{}] with issuer [{}]", claims, claims.getIssuer());
        val iss = resolveIssuer(service);
        Objects.requireNonNull(iss, "Issuer cannot be null or undefined");
        FunctionUtils.throwIf(!claims.getIssuer().equalsIgnoreCase(iss),
            () -> new IllegalArgumentException("Issuer assigned to JWT claim " + claims.getIssuer() + " does not match " + iss));
    }
Gets allowed signing algorithms.
Returning an empty collection indicates that all algorithms should be supported, except none.

@param registeredService the svc
@return the allowed signing algorithms
support/cas-server-support-oauth-core-api/src/main/java/org/apereo/cas/ticket/BaseTokenSigningAndEncryptionService.java