In this section, we will explore how to use PowerShell to interact with REST APIs. REST (Representational State Transfer) APIs are a common way to enable communication between different software systems over HTTP. PowerShell, with its powerful scripting capabilities, can be an excellent tool for automating tasks that involve REST APIs.

1. REST API Basics:

   • Endpoints: URLs that represent the resources you want to interact with.
   • HTTP Methods: Common methods include GET (retrieve data), POST (send data), PUT (update data), DELETE (remove data).
   • Headers: Metadata sent with the request, such as authentication tokens.
   • Body: Data sent with POST or PUT requests, often in JSON format.

2. PowerShell Cmdlets for HTTP Requests:

   • Invoke-RestMethod: Simplifies interaction with REST APIs by automatically parsing JSON responses.
   • Invoke-WebRequest: Provides more control over the HTTP request and response but requires manual parsing of JSON.

Let's start with a simple GET request to retrieve data from a public API.

Explanation:

• $apiUrl contains the URL of the API endpoint.
• Invoke-RestMethod sends a GET request to the specified URL.
• The response is stored in the $response variable and then displayed.

Next, let's make a POST request to send data to an API. For this example, we'll use a mock API that accepts JSON data.

Explanation:

• $postData is a hashtable containing the data to send, which is then converted to JSON using ConvertTo-Json.
• Invoke-RestMethod sends a POST request with the JSON data in the body.
• The response is stored in the $response variable and then displayed.

Many APIs require authentication. Here's an example of making an authenticated GET request using an API key.

Explanation:

• $headers is a hashtable containing the authorization header with the API key.
• Invoke-RestMethod sends a GET request with the specified headers.

Task: Use the GitHub API to fetch and display information about a specific user.

Instructions:

1. Define the API endpoint for fetching user data (e.g., https://api.github.com/users/{username}).
2. Replace {username} with a GitHub username of your choice.
3. Use Invoke-RestMethod to make the GET request.
4. Display the user's name, public repositories count, and followers count.

Solution:

Task: Use a mock API to create a new resource by sending a POST request with JSON data.

Instructions:

1. Define the API endpoint for creating a new resource (e.g., https://jsonplaceholder.typicode.com/posts).
2. Create a hashtable with the data to send (e.g., title, body, userId).
3. Convert the hashtable to JSON.
4. Use Invoke-RestMethod to make the POST request.
5. Display the response.

Solution:

• Incorrect URL: Ensure the API endpoint URL is correct and accessible.
• Authentication Errors: Verify that the authentication method and credentials are correct.
• JSON Formatting: Use ConvertTo-Json to ensure the data is correctly formatted as JSON.
• Error Handling: Use try and catch blocks to handle errors gracefully.

In this section, we covered the basics of using PowerShell to interact with REST APIs. We learned how to make GET and POST requests, handle authentication, and parse JSON responses. By practicing with the provided exercises, you should now be more comfortable using PowerShell to automate tasks involving REST APIs. In the next module, we will delve into more advanced PowerShell features, including creating and using classes.