Are there any public web services that will check for an MTLS cert and response with application/json

Question

A different thread pointed out a couple of services that would require a client MTLS certificate, accept any cert, and then respond with information about the SSL handshake/certs.

HTTPS test server that checks client certificates

These endpoints both return HTML. Does anyone know of anything similar that returns application/json?

Answer 1

The URLs below will return application/json content upon successfully mutual TLS client certificate authentication. If no authentication is peformed, then HTTP error 403 is returned in the HTTP headers and the response is empty:

• https://certauth.idrix.fr/json (TLS 1.2 only)
• https://certauth.cryptomix.com/json (TLS 1.2 and TLS 1.3)

The json returned in case of success contains various technical information about the established connection.