How do I secure the access token by directly calling API Gateway's REST APIs?

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About this task

This section explains how to secure the get access token calls when you enforce the PKCE using REST APIs.

Before you begin

Ensure that you have:

generated Code Challenge and Code Verifier using the JAR file. For details about how to generate code challenge and code verifier, see How do I generate code verifier and code challenge using JAR files?.
enforced PKCE either at global level or application level.

To secure the access token

Procedure

Get authorization code.
1. Call the authorize endpoint using a REST client. http(s)://hostname:port/invoke/pub.apigateway.oauth2/authorize? response_type=code&redirect_uri=<redirectURI>&client_id=<Client ID>&code_challenge=<Code_Challenge>&code_challenge_method=S256
  
  Note: Make sure you have replaced the redirectURI , ClientID, and Code_Challenge in the above mentioned URL. You can get the redirect URI and client ID from the Authentication tab of the Application screen.
2. Click the Approve button
3. Provide the credentials of API Gateway user to approve the request.
  
  You are re-directed to the redirect URI as per the configuration in the application strategy. The screenshot below is just a sample, you are redirected to a different URL based on your configuration, so the screenshot varies accordingly. If the given redirect URI is not a valid web page, you might get a Page not found error, which is fine, because we get the authorization code value from the browser URL.
4. Make a note of the authorization code.
  
  Note: If the redirect URL screen is not able to display the authorization code, then you can take it from the address bar of the browser. As highlighted in the above image's URL, you can see the authorization code in the code=field of the URL.
Get access token.
1. Invoke the access token endpoint using a REST client.
  Request: POST http(s)://hostname:port/invoke/pub.apigateway.oauth2/getAccessToken.
  You need to pass authorization header using basic authentication with the client ID as username and client secret as the password. You can get the client ID and client secret in the Authentication tab of the Application screen in the API Gateway UI.
  Sample request body
```
{
               "redirect_uri":"http://test.com",
               "scope":"email",
               "grant_type":"authorization_code", 
               "code":"0025abe9f96d4901b61340344c29a576",
               "code_verifier":"a4793f15479a4c5697f93b44d055ab6cbd16be50400a4591892f914b1a256da8",
               "client_id":"374b1fae-4405-411b-85a0-6e1ab90923ba"
} 
```
  Note: You must replace the redirect_URI, scope, code, and code_verifier with appropriate values. For the code field, make sure you use the authorization code you noted down in the step 1.d.
  Sample response body
```
{
    "access_token": "b5b33bc9c57945f388010f8caf5fe9b6b14abef468d346e68e0cd374c0df60d7",
    "token_type": "Bearer",
    "expires_in": 3600
}
```