Updates Backstage auth to exercise (#494)

* Updates the backstage documentation to reflect the new backend system.

* Fixes typo

docs/9-platform-engineering/9.1-backstage.md

@@ -71,6 +71,7 @@ a GitHub org to play around with. Each person going through the bootcamp will ne
 ### Exercise 2: Stand up local instance of Backstage
 
 1. Follow Backstage's official [Getting Started](https://backstage.spotify.com/learn/standing-up-backstage/standing-up-backstage/1-intro/) guide
+> Skip setting up the PostgresSQL instance
 2. Start your local instance of Backstage and get familiar with the UI
 3. Customize the look and feel of you backstage instance
     - Change the logo
@@ -80,15 +81,12 @@ a GitHub org to play around with. Each person going through the bootcamp will ne
 
 ### Exercise 3: Configure Authentication via GitHub
 
-Currently your backstage instance is not authenticating the user. You are an anonymous guest. Given that an IDP will have access to all the engineering resources in an organization and have access to self-service resources we need to add authentication. Backstage's authentication system servers a couple of purposes. First it is there for sign-in functionality and to authenticate the user. Additionally it can be used to grant access to third-party resources. Typically you will use one authentication provider for sing-in functionality and other authentication providers will be used to grant access to third-party resources.
+Currently your backstage instance is not authenticating the user. You are an anonymous guest. Given that an IDP will have access to all the engineering resources in an organization and have access to self-service resources we need to add authentication. Backstage's authentication system servers a couple of purposes. First it is there for sign-in functionality and to authenticate the user. Additionally it can be used to grant access to third-party resources. Typically you will use one authentication provider for sign-in functionality and other authentication providers will be used to grant access to third-party resources.
 
-1. Create an Oauth app for your GitHub Organization
-2. Configure Backstage to authenticate with GitHub
+1. Configure Backstage to authenticate with GitHub
 > Do not store secrets in plain text that will be pushed to your remote repo!
-3. Add GitHub Authentication to the Sign-In page
-4. Verify that you can login via GitHub
-
-<!-- ## Extra Credit: Three Musketeers Pattern -->
+2. Add GitHub Authentication to the Sign-In page
+3. Verify that you can login via GitHub
 
 ## Deliverables