A lot of the authentication is TLS client certificate authentication, SAML hosted by internal SAML IdP systems (such as ADFS) for web stuff. For most other thi

A lot of the authentication is TLS client certificate authentication, SAML hosted by internal SAML IdP systems (such as ADFS) for web stuff. For most other things Kerberos (via PKINIT) is used. SSH authentication X.509 using PKIXSSH is rarely used since it is not a standard part of any operating systems used. For SSH, typically either Kerberos or SSH keys based on the RSA keys used by the certificates.