docs: update auth docs to mention and prefer single-provider SignInPage

docs/auth/index.md

@@ -86,7 +86,8 @@ to a `guest` identity for all users, without any ID token. To enable sign-in, a
 `SignInPage` needs to be configured, which in turn has to supply a user to the
 app. The `@backstage/core` package provides a basic sign-in page that allows
 both the user and the app developer to choose between a couple of different
-sign-in methods.
+sign-in methods, or to designate a single provider that may also be logged in to
+automatically.
 
 ## Further Reading
 

docs/tutorials/quickstart-app-auth.md

@@ -349,22 +349,18 @@ const app = createApp({
   apis,
   plugins: Object.values(plugins),
   components: {
-    SignInPage: props => {
-      return (
-        <SignInPage
-          {...props}
-          providers={[
-            {
-              id: 'github-auth-provider',
-              title: 'GitHub',
-              message: 'Simple Backstage Application Login',
-              apiRef: githubAuthApiRef,
-            },
-          ]}
-          align="center"
-        />
-      );
-    },
+    SignInPage: props => (
+      <SignInPage
+        {...props}
+        auto
+        provider={{
+          id: 'github-auth-provider',
+          title: 'GitHub',
+          message: 'Simple Backstage Application Login',
+          apiRef: githubAuthApiRef,
+        }}
+      />
+    ),
   },
 });
 ```