Update switch-auth.mdx (#5455)

Updated "back-end" to "backend"
Updated "Setup" to "Set up" ("set up" is two words when used as a compound verb)

Author: hibler13

src/fragments/lib/auth/js/switch-auth.mdx

@@ -3,7 +3,7 @@ For client side authentication there are three different flows:
 
 1. `USER_SRP_AUTH`: The `USER_SRP_AUTH` flow uses the [SRP protocol (Secure Remote Password)](https://en.wikipedia.org/wiki/Secure_Remote_Password_protocol) where the password never leaves the client and is unknown to the server. This is the recommended flow and is used by default.
 
-2. `USER_PASSWORD_AUTH`: The `USER_PASSWORD_AUTH` flow will send user credentials unencrypted to the back-end. If you want to migrate users to Cognito using the "Migration" trigger and avoid forcing users to reset their passwords, you will need to use this authentication type because the Lambda function invoked by the trigger needs to verify the supplied credentials.
+2. `USER_PASSWORD_AUTH`: The `USER_PASSWORD_AUTH` flow will send user credentials unencrypted to the backend. If you want to migrate users to Cognito using the "Migration" trigger and avoid forcing users to reset their passwords, you will need to use this authentication type because the Lambda function invoked by the trigger needs to verify the supplied credentials.
 
 3. `CUSTOM_AUTH`: The `CUSTOM_AUTH` flow is used to allow for a series of challenge and response cycles that can be customized to meet different requirements.
 
@@ -23,7 +23,7 @@ Auth.configure({
 
 A use case for the `USER_PASSWORD_AUTH` authentication flow is migrating users into Amazon Cognito
 
-### Setup auth backend
+### Set up auth backend
 
 In order to use the authentication flow `USER_PASSWORD_AUTH`, your Cognito app client has to be configured to allow it. In the AWS Console, this is done by ticking the checkbox at General settings > App clients > Show Details (for the affected client) > Enable username-password (non-SRP) flow. If you're using the AWS CLI or CloudFormation, update your app client by adding `USER_PASSWORD_AUTH` to the list of "Explicit Auth Flows".
 
@@ -130,4 +130,4 @@ export const handler = async (event, context) => {
 
   return event;
 };
-```
+```