[ADF-1586] Added auth guard docs (#2624)

docs/auth-guard.service.md

@@ -0,0 +1,44 @@
+# Auth Guard service
+
+Adds authentication to a route within the app.
+
+## Details
+
+The Auth Guard service implements an Angular
+[route guard](https://angular.io/guide/router#milestone-5-route-guards)
+to check the user is logged in. This is typically used with the
+`canActivate` guard check in the route definition:
+
+```ts
+const appRoutes: Routes = [
+    ...
+    {
+        path: 'examplepath',
+        component: ExampleComponent,
+        canActivate: [ AuthGuard ]      // <- Requires authentication for this route.
+    },
+    ...
+]
+```
+
+If the user now clicks on a link or button that follows this route, they will be prompted
+to log in before proceeding.
+
+This service will accept authentication with either APS or ACS as valid and is thus suitable for
+menu pages and other content that doesn't make use of APS or ACS features. Use the
+[Auth Guard Bpm service](auth-guard-bpm.service.md) and
+[Auth Guard Ecm service](auth-guard-ecm.service.md) to authenticate
+against APS or ACS, respectively. See the
+[ADF custom page tutorial](https://community.alfresco.com/docs/DOC-6628-adf-105-creating-custom-pages-and-components)
+for worked examples of all three guards.
+
+<!-- Don't edit the See also section. Edit seeAlsoGraph.json and run config/generateSeeAlso.js -->
+<!-- seealso start -->
+## See also
+
+- [Auth guard bpm service](auth-guard-bpm.service.md)
+- [Auth guard ecm service](auth-guard-ecm.service.md)
+<!-- seealso end -->
+
+
+