public X509Certificate getEndEntityCertificate( Certificate chain[] )
    {
        if ( chain == null || chain.length == 0 )
        {
            return null;
        }

        final X509Certificate first = (X509Certificate) chain[ 0 ];
        try
        {
            first.checkValidity();
        }
        catch ( CertificateException e )
        {
            Log.warn( "EE Certificate not valid: " + e.getMessage() );
            return null;
        }

        if ( chain.length == 1 && first.getSubjectX500Principal().equals( first.getIssuerX500Principal() ) )
        {
            // Chain is single cert, and self-signed.
            try
            {
                if ( store.getCertificateAlias( first ) != null )
                {
                    // Interesting case: trusted self-signed cert.
                    return first;
                }
            }
            catch ( KeyStoreException e )
            {
                Log.warn( "Keystore error while looking for self-signed cert; assuming untrusted." );
            }
            return null;
        }

        final List<Certificate> allCerts = new ArrayList<>();
        try
        {
            // Add the trusted certs.
            for ( Enumeration<String> aliases = store.aliases(); aliases.hasMoreElements(); )
            {
                String alias = aliases.nextElement();
                if ( store.isCertificateEntry( alias ) )
                {
                    X509Certificate cert = (X509Certificate) store.getCertificate( alias );
                    allCerts.add( cert );
                }
            }

            // Finally, add all the certs in the chain:
            allCerts.addAll( Arrays.asList( chain ) );

            final CertStore cs = CertStore.getInstance( "Collection", new CollectionCertStoreParameters( allCerts ) );
            final X509CertSelector selector = new X509CertSelector();
            selector.setCertificate( first );
            // / selector.setSubject(first.getSubjectX500Principal());

            final PKIXBuilderParameters params = new PKIXBuilderParameters( store, selector );
            params.addCertStore( cs );
            params.setDate( new Date() );
            params.setRevocationEnabled( false );

            /* Code here is the right way to do things. */
            final CertPathBuilder pathBuilder = CertPathBuilder.getInstance( CertPathBuilder.getDefaultType() );
            final CertPath cp = pathBuilder.build( params ).getCertPath();

            /*
             * This section is an alternative to using CertPathBuilder which is not as complete (or safe), but will emit
             * much better errors. If things break, swap around the code.
             *
             **** COMMENTED OUT. ****
             *
            final List<X509Certificate> ls = new ArrayList<>();
            for ( final Certificate cert : chain )
            {
                ls.add( (X509Certificate) cert );
            }

            for ( X509Certificate last = ls.get( ls.size() - 1 );
                  !last.getIssuerX500Principal().equals( last.getSubjectX500Principal() );
                  last = ls.get( ls.size() - 1 ) )
            {
                final X509CertSelector sel = new X509CertSelector();
                sel.setSubject( last.getIssuerX500Principal() );
                ls.add( (X509Certificate) cs.getCertificates( sel ).toArray()[ 0 ] );
            }
            final CertPath cp = CertificateFactory.getInstance( "X.509" ).generateCertPath( ls );
             ****** END ALTERNATIVE. ****
             */

            // Not entirely sure if I need to do this with CertPathBuilder. Can't hurt.
            final CertPathValidator pathValidator = CertPathValidator.getInstance( "PKIX" );
            pathValidator.validate( cp, params );

            return (X509Certificate) cp.getCertificates().get( 0 );
        }
        catch ( CertPathBuilderException e )
        {
            Log.warn( "Path builder exception while validating certificate chain:", e );
        }
        catch ( CertPathValidatorException e )
        {
            Log.warn( "Path exception while validating certificate chain:", e );
        }
        catch ( Exception e )
        {
            Log.warn( "Unknown exception while validating certificate chain:", e );
        }
        return null;
    }
Decide whether or not to trust the given supplied certificate chain, returning the
End Entity Certificate in this case where it can, and null otherwise.
A self-signed certificate will, for example, return null.
For certain failures, we SHOULD generate an exception - revocations and the like,
but we currently do not.

@param chain an array of X509Certificate where the first one is the endEntityCertificate.
@return trusted end-entity certificate, or null.
xmppserver/src/main/java/org/jivesoftware/openfire/keystore/TrustStore.java