This case-sensitive code system http://hl7.org/fhir/us/davinci-pdex/CodeSystem/EndpointAccessControlMechanismCS defines the following codes:

Code	Display	Definition
public	Public	Public
opaque-access-token	Opaque Access Token	Opaque Access Token
jwt-access-token	JWT Access Token	JWT Access Token
mutual-tls	Mutual TLS	Mutual TLS
wss-saml-token	WSS SAML Token	WSS SAML Token
wss-username-token	WSS User Name Token	WSS User Name Token
wss-kerberos-token	WSS Kerberos Token	WSS Kerberos Token
wss-x509-token	WSS X509 Token	WSS X509 Token
wss-custom-token	WSS Custom Token	WSS Custom Token