docs: fix typos in the documentation (#2633)

docs/auth/index.md

@@ -6,7 +6,7 @@ description: Documentation on User Authentication and Authorization in Backstage
 
 ## Summary
 
-The purpose of the Auth APIs in Backstage are to identify the user, and to
+The purpose of the Auth APIs in Backstage is to identify the user, and to
 provide a way for plugins to request access to 3rd party services on behalf of
 the user (OAuth). This documentation focuses on the implementation of that
 solution and how to extend it. For documentation on how to consume the Auth APIs

docs/auth/oauth.md

@@ -52,7 +52,7 @@ in a new popup window that is opened by the app. By using a popup-based flow it
 is possible to request authentication at any point in the app, without requiring
 a redirect. Because of this there is no need to ask for all scopes upfront, or
 interrupt the app with a redirect and forcing plugin authors to take care in
-restoring state after a redirect has been make. All in all it makes it much
+restoring state after a redirect has been made. All in all it makes it much
 easier to make authenticated requests inside a plugin.
 
 ## OAuth Flow
@@ -67,7 +67,7 @@ Component and APIs can request Access or ID Tokens from any available Auth
 provider. If there already exists a cached fresh token that covers (at least)
 the requested scopes, it will be returned immediately. If the OAuth provider
 implements token refreshes, this check will also trigger a token refresh attempt
-if no session is a available.
+if no session is available.
 
 If new scopes are requested, or the user is not yet logged in with that
 provider, a dialog is shown informing the user that they need to log in with the