Bug 1782080 - Generalize preference gates of the Credential Management API, r=dveditz,emilio

I'm looking to implement the FedCM browser API, which hooks into the Credentail Management API.
Just cleaning up a few preference-gates in webidl and adding new preferences to use as gates.

Differential Revision: https://phabricator.services.mozilla.com/D153586

dom/webidl/CredentialManagement.webidl

@@ -5,15 +5,19 @@
  *
  * The origin of this IDL file is
  * https://www.w3.org/TR/credential-management-1/
+ * and
+ * https://w3c.github.io/webauthn/
+ * and
+ * https://fedidcg.github.io/FedCM/
  */
 
-[Exposed=Window, SecureContext, Pref="security.webauth.webauthn"]
+[Exposed=Window, SecureContext]
 interface Credential {
   readonly attribute USVString id;
   readonly attribute DOMString type;
 };
 
-[Exposed=Window, SecureContext, Pref="security.webauth.webauthn"]
+[Exposed=Window, SecureContext]
 interface CredentialsContainer {
   [NewObject]
   Promise<Credential?> get(optional CredentialRequestOptions options = {});
@@ -26,13 +30,19 @@ interface CredentialsContainer {
 };
 
 dictionary CredentialRequestOptions {
-  // FIXME: bug 1493860: should this "= {}" be here?
-  PublicKeyCredentialRequestOptions publicKey = {};
+  // This is taken from the partial definition in
+  // https://w3c.github.io/webauthn/#sctn-credentialrequestoptions-extension
+  [Pref="security.webauth.webauthn"]
+  PublicKeyCredentialRequestOptions publicKey;
+  [Pref="dom.security.credentialmanagement.identity.enabled"]
+  IdentityCredentialRequestOptions identity;
   AbortSignal signal;
 };
 
 dictionary CredentialCreationOptions {
-  // FIXME: bug 1493860: should this "= {}" be here?
-  PublicKeyCredentialCreationOptions publicKey = {};
+  // This is taken from the partial definition in
+  // https://w3c.github.io/webauthn/#sctn-credentialcreationoptions-extension
+  [Pref="security.webauth.webauthn"]
+  PublicKeyCredentialCreationOptions publicKey;
   AbortSignal signal;
 };

modules/libpref/init/StaticPrefList.yaml

@@ -3638,6 +3638,12 @@
   value: false
   mirror: always
 
+# pref controls `identity` credentials being exposed
+- name: dom.security.credentialmanagement.identity.enabled
+  type: bool
+  value: false
+  mirror: always
+
 # Whether or not selection events on text controls are enabled.
 - name: dom.select_events.textcontrols.selectionchange.enabled
   type: bool