docs: scaffolder: improve docs to setup the RepoUrlPicker authentication

Signed-off-by: Maixmilian Ressel <maximiliandotressel@gmail.com>

docs/auth/index.md

@@ -185,6 +185,24 @@ const app = createApp({
 When using multiple auth providers like this, it's important that you configure the different
 sign-in resolvers so that they resolve to the same identity regardless of the method used.
 
+## Scaffolder Configuration (Software Templates)
+
+If you want to use the authentication capabilities of the [Repository Picker](../features/software-templates/writing-templates.md#the-repository-picker) inside your Software Templates you will need to configure the [`ScmAuthApi`](https://backstage.io/docs/reference/integration-react.scmauthapi) alongside your authentication provider. It is an API used to authenticate towards different SCM systems in a generic way, based on what resource is being accessed.
+
+To set it up, you'll need to add an API factory entry to `packages/app/src/apis.ts`. The example below sets up the `ScmAuthApi` for an already configured GitLab authentication provider:
+
+```ts
+createApiFactory({
+  api: scmAuthApiRef,
+  deps: {
+    gitlabAuthApi: gitlabAuthApiRef,
+  },
+  factory: ({ gitlabAuthApi }) => ScmAuth.forGitlab(gitlabAuthApi),
+});
+```
+
+In case you are using a custom authentication providers, you might need to add a [custom `ScmAuthApi` implementation](./index.md#custom-scmauthapi-implementation).
+
 ## For Plugin Developers
 
 The Backstage frontend core APIs provide a set of Utility APIs for plugin developers

docs/features/software-templates/writing-templates.md

@@ -397,6 +397,9 @@ There's also the ability to pass additional scopes when requesting the `oauth`
 token from the user, which you can do on a per-provider basis, in case your
 template can be published to multiple providers.
 
+Note, that you will need to configure an [authentication provider](../../auth/index.md#configuring-authentication-providers), alongside the
+[`ScmAuthApi`](../../auth/index.md#scaffolder-configuration-software-templates) for your source code management (scm) service to make this feature work.
+
 ### Accessing the signed-in users details
 
 Sometimes when authoring templates, you'll want to access the user that is running the template, and get details from the profile or the users `Entity` in the Catalog.