feat(xo-server): passport strategies can be unregistered (#4702)

Now all authentication plugins can be unloaded.

packages/xo-server-auth-saml/src/index.js

@@ -48,6 +48,7 @@ You should try \`http://schemas.xmlsoap.org/ws/2005/05/identity/claims/emailaddr
 class AuthSamlXoPlugin {
   constructor({ xo }) {
     this._conf = null
+    this._unregisterPassportStrategy = undefined
     this._usernameField = null
     this._xo = xo
   }
@@ -66,7 +67,7 @@ class AuthSamlXoPlugin {
   load() {
     const xo = this._xo
 
-    xo.registerPassportStrategy(
+    this._unregisterPassportStrategy = xo.registerPassportStrategy(
       new Strategy(this._conf, async (profile, done) => {
         const name = profile[this._usernameField]
         if (!name) {
@@ -83,6 +84,10 @@ class AuthSamlXoPlugin {
       })
     )
   }
+
+  unload() {
+    this._unregisterPassportStrategy()
+  }
 }
 
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