I am trying to make an API call to an external resource using the https/clientCertificate Module, but the module only works for POST requests. I am assuming the answer is no, but does anyone know of any workaround to this limitation, besides using a middleware?

that's strange but good to know. Since the SSL handshake does authentication before the HTTP request happens I'm surprised it's limited to HTTP POST (or any other specific HTTP verb). I haven't used it but I assume that module is just doing TLS client auth in addition to server auth?

I am honestly not sure what its doing behind the scenes. I am going to open a case, but I doubt there is going to be any work around