I host a website that uses mTLS for authentication. I created a client cert and installed it in Firefox on Linux, and when I visit the site for the first time, Firefox asks me to choose my cert and then I’m able to visit the site (and every subsequent visit to the site is successful without having to select the cert each time). This is all good.

But when I install that client cert into GrapheneOS (settings -> encryption & credentials -> install a certificate -> vpn & app user certificate), no browser app seems to recognize that it exists at all. Visiting the website from Vanadium, Fennec, or Mull browsers all return “ERR_BAD_SSL_CLIENT_AUTH_CERT” errors.

Does anyone have experience successfully using an mTLS cert in GrapheneOS?