private Set<TrustAnchor> findAllTrustAnchorsByIssuerAndSignature(X509Certificate cert) {
        Set<TrustAnchor> indexedAnchors =
                trustedCertificateIndex.findAllByIssuerAndSignature(cert);
        if (!indexedAnchors.isEmpty() || trustedCertificateStore == null) {
            return indexedAnchors;
        }
        Set<X509Certificate> storeAnchors = trustedCertificateStore.findAllIssuers(cert);
        if (storeAnchors.isEmpty()) {
            return indexedAnchors;
        }
        Set<TrustAnchor> result = new HashSet<>(storeAnchors.size());
        for (X509Certificate storeCert : storeAnchors) {
            result.add(trustedCertificateIndex.index(storeCert));
        }
        return result;
    }
Find all possible issuing trust anchors of {@code cert}.
common/src/main/java/org/conscrypt/TrustManagerImpl.java