message: improve the Custom ScmAuthApi Implementation section of docs/auth
diff: @@ -260,7 +260,18 @@ Passport-supported authentication method.
  If you are using any custom authentication providers, like for example one for GitHub Enterprise, then you are likely to need a custom implementation of the [`ScmAuthApi`](https://backstage.io/docs/reference/integration-react.scmauthapi). It is an API used to authenticate towards different SCM systems in a generic way, based on what resource is being accessed, and is used for example by the Scaffolder (Software Templates) and Catalog Import plugins.
  -To set up a custom `ScmAuthApi` implementation, you'll need to add an API factory entry to `packages/app/src/apis.ts`. The following example shows an implementation that supports both public GitHub via `githubAuthApi` as well as a GitHub Enterprise installation hosted at `ghe.example.com` via `gheAuthApi`:
  +To set up a custom `ScmAuthApi` implementation, you'll will need to complete the following steps which creates an example entry for a github enterprise installation:
  +
  +1. Create an additional `xxxAuthApiRef` which can be defined either inside the app itself if it's only used for this purpose, or inside an internal common package for APIs, such as `@internal/apis`:
  +
  + ```ts
  + const gheAuthApiRef: ApiRef<OAuthApi & ProfileInfoApi & SessionApi> =
  + createApiRef({
  + id: 'internal.auth.ghe',
  + });
  + ```
  +
  +2. Add an API factory entry to `packages/app/src/apis.ts`. The following example shows an implementation that supports both public GitHub via `githubAuthApi` as well as a GitHub Enterprise installation hosted at `ghe.example.com` via `gheAuthApi`:
  ```ts
  createApiFactory({
  @@ -278,3 +289,16 @@ createApiFactory({
  ),
  });
  ```
  +_**Warning:** You will need to remove the default `ScmAuth.createDefaultApiFactory();` with this approach.
  +
  +3. Finally you also need to add and configure another GitHub provider to the `auth-backend` using the provider ID, which in this example is `ghe`:
  +
  +
  + ```ts
  + import { providers } from '@backstage/plugin-auth-backend';
  +
  + // Add the following options to `createRouter` in packages/backend/src/plugins/auth.ts
  + providerFactories: {
  + ghe: providers.github.create(),
  + },
  + ```
  \ No newline at end of file
  