REST API Calls

PowerShell provides robust tools for interacting with RESTful APIs through Invoke-RestMethod and Invoke-WebRequest. These cmdlets enable you to send HTTP requests (GET, POST, PUT, DELETE, etc.) to web services, parse responses, and integrate with enterprise systems like cloud platforms, custom APIs, or third-party services. This section covers core concepts and practical examples for making REST API calls.

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Choosing Between Invoke-RestMethod and Invoke-WebRequest

• Invoke-RestMethod
  Simplifies working with JSON-based APIs. It automatically serializes/deserializes data and handles common HTTP methods. Best for straightforward REST interactions.
  Example:
  

  $response = Invoke-RestMethod -Uri "https://api.example.com/data" -Method Get
  

• Invoke-WebRequest
  Offers finer control over raw HTTP requests and responses. Useful for non-JSON payloads, custom headers, or advanced scenarios like file uploads.
  Example:
  

  $response = Invoke-WebRequest -Uri "https://api.example.com/data" -Method Get
  $content = $response.Content | ConvertFrom-Json
  

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Core Concepts: HTTP Verbs and Parameters

Verb	Purpose	Example Command
GET	Retrieve data	Invoke-RestMethod -Uri "https://api.example.com/users" -Method Get
POST	Create a resource	Invoke-RestMethod -Uri "https://api.example.com/users" -Method Post -Body $userData
PUT	Update a resource	Invoke-RestMethod -Uri "https://api.example.com/users/123" -Method Put -Body $userData
DELETE	Remove a resource	Invoke-Rest,Method -Uri "https://api.example.com/users/123" -Method Delete

Key Parameters:
- -Uri: Target API endpoint.
- -Method: HTTP verb (Get, Post, etc.).
- -Headers: Add custom headers (e.g., for authentication).
- -Body: Data to send in the request body (use -ContentType to specify format like application/json).

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Example: Authenticating with a Bearer Token

$token = "your-access-token"
$headers = @{
    "Authorization" = "Bearer $token"
    "Accept"        = "application/json"
}

$response = Invoke-RestMethod -Uri "https://api.example.com/secure/data" -Headers $headers -Method Get

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Handling Errors and Responses

• Error Handling: Use try/catch blocks to handle exceptions:
  

  try {
      $response = Invoke-RestMethod -Uri "https://api.example.com/data" -Method Get
  } catch {
      Write-Error "API request failed: $_"
  }
  

• Parsing Responses:
  For JSON responses, use ConvertFrom-Json to transform raw content into PowerShell objects.
  

  $users = $response.Content | ConvertFrom-Json
  

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Common Use Cases

1. Automating Cloud Services: Interact with AWS, Azure, or GCP APIs to manage resources.
2. Custom API Integration: Communicate with internal systems or SaaS platforms.
3. Monitoring and Reporting: Poll APIs for metrics or log data.

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Key takeaways

• Use Invoke-RestMethod for simplicity with JSON APIs; use Invoke-WebRequest for raw HTTP control.
• Always specify -Method and handle authentication via headers.
• Parse JSON responses with ConvertFrom-Json and use try/catch for error resilience.
• Leverage PowerShell’s object-oriented approach to work with API data directly.
• Test endpoints with tools like Postman before automating to ensure correct request formats.