src/main/java/com/authlete/jaxrs/BaseEndpoint.java
protected String extractClientCertificate(HttpServletRequest request)
    {
        String[] certs = extractClientCertificateChain(request);

        if (certs != null && certs.length > 0)
        {
            return certs[0];
        }
        else
        {
            return null;
        }
    }
protected String extractClientCertificate(HttpServletRequest request)
    {
        String[] certs = extractClientCertificateChain(request);

        if (certs != null && certs.length > 0)
        {
            return certs[0];
        }
        else
        {
            return null;
        }
    }
Utility method for extracting a single client certificate from the default
certificate extractors. Calls extractClientCertificateChain and returns the
first entry in the array, if any, null otherwise.

@param request
The incoming HTTP request to search for the client's certificate.

@return
The client's mutual TLS certificate.

@since 2.8