github app: generate jwt with powershell (#30679)

Co-authored-by: Sarah Edwards <skedwards88@github.com>

Author: mac2000

content/apps/creating-github-apps/authenticating-with-a-github-app/generating-a-json-web-token-jwt-for-a-github-app.md

@@ -175,3 +175,32 @@ signature=$(
 JWT="${header_payload}"."${signature}"
 printf '%s\n' "JWT: $JWT"
 ```
+
+### Example: Using PowerShell to generate a JWT
+
+In the following example, replace `YOUR_PATH_TO_PEM` with the file path where your private key is stored. Replace `YOUR_APP_ID` with the ID of your app. Make sure to enclose the values for `YOUR_PATH_TO_PEM` in double quotes.
+
+```powershell copy
+#!/usr/bin/env pwsh
+
+$app_id = YOUR_APP_ID
+$private_key_path = "YOUR_PATH_TO_PEM"
+
+$header = [Convert]::ToBase64String([System.Text.Encoding]::UTF8.GetBytes((ConvertTo-Json -InputObject @{
+  alg = "RS256"
+  typ = "JWT"
+}))).TrimEnd('=').Replace('+', '-').Replace('/', '_');
+
+$payload = [Convert]::ToBase64String([System.Text.Encoding]::UTF8.GetBytes((ConvertTo-Json -InputObject @{
+  iat = [System.DateTimeOffset]::UtcNow.AddSeconds(-10).ToUnixTimeSeconds()  
+  exp = [System.DateTimeOffset]::UtcNow.AddMinutes(10).ToUnixTimeSeconds()
+  iss = $app_id    
+}))).TrimEnd('=').Replace('+', '-').Replace('/', '_');
+
+$rsa = [System.Security.Cryptography.RSA]::Create()
+$rsa.ImportFromPem((Get-Content $private_key_path -Raw))
+
+$signature = [Convert]::ToBase64String($rsa.SignData([System.Text.Encoding]::UTF8.GetBytes("$header.$payload"), [System.Security.Cryptography.HashAlgorithmName]::SHA256, [System.Security.Cryptography.RSASignaturePadding]::Pkcs1)).TrimEnd('=').Replace('+', '-').Replace('/', '_')
+$jwt = "$header.$payload.$signature"
+Write-Host $jwt
+```