Add LoginToGH script

eng/common/scripts/LoginToGH.ps1

@@ -0,0 +1,157 @@
+<#
+.SYNOPSIS
+  Mints a GitHub App installation access token using Azure Key Vault 'sign' (non-exportable key),
+  and logs in the GitHub CLI by setting GH_TOKEN (and GITHUB_TOKEN).
+
+.PARAMETER KeyVaultName
+  Name of the Azure Key Vault containing the non-exportable RSA key.
+
+.PARAMETER KeyName
+  Name of the RSA key in Key Vault (imported as a *key*, not a secret).
+
+.PARAMETER GitHubAppId
+  Numeric App ID (not client ID) of your GitHub App.
+
+.PARAMETER PipelineVariableName
+  Name of the ADO variable to set when -SetPipelineVariable is used (default: GH_TOKEN).
+
+.OUTPUTS
+  Writes minimal info to stdout. Token is placed in $env:GH_TOKEN and $env:GITHUB_TOKEN.
+
+.NOTES
+  Requires: Azure CLI (az), git (optional), gh (optional if ShowGhAuthStatus is used).
+#>
+
+[CmdletBinding()]
+param(
+  [string] $KeyVaultName = "azuresdkengkeyvault",
+  [string] $KeyName = "azure-sdk-automation",
+  [string] $GitHubAppId = '1086291',
+  [string] $InstallationTokenOwner = "Azure",
+  [string] $PipelineVariableName = "GH_TOKEN"
+)
+
+$ErrorActionPreference = 'Stop'
+Set-StrictMode -Version Latest
+
+$GitHubApiBaseUrl = "https://api.github.com"
+$GitHubApiVersion = "2022-11-28"
+
+function Get-Headers {
+  param(
+    [Parameter(Mandatory)][string] $Jwt,
+    [Parameter(Mandatory)][string] $ApiVersion
+  )
+  return @{
+    'Authorization'        = "Bearer $Jwt"
+    'Accept'               = 'application/vnd.github+json'
+    'X-GitHub-Api-Version' = $ApiVersion
+    'User-Agent'           = 'ado-pwsh-ghapp'
+  }
+}
+
+function New-GitHubAppJwt {
+  param(
+    [Parameter(Mandatory)] [string] $VaultName,
+    [Parameter(Mandatory)] [string] $KeyName,
+    [Parameter(Mandatory)] [string] $AppId
+  )
+
+  function Base64UrlEncode($json) {
+    $bytes = [System.Text.Encoding]::UTF8.GetBytes($json)
+    $base64 = [Convert]::ToBase64String($bytes)
+    return $base64.TrimEnd('=') -replace '\+', '-' -replace '/', '_'
+  }
+
+  # === STEP 1: Create JWT Header and Payload ===
+  $Header = @{
+      alg = "RS256"
+      typ = "JWT"
+  }
+  $Now = [int][double]::Parse((Get-Date -UFormat %s))
+  $Payload = @{
+      iat = $Now
+      exp = $Now + 600  # 10 minutes
+      iss = $AppId
+  }
+
+  $EncodedHeader = Base64UrlEncode (ConvertTo-Json $Header -Compress)
+  $EncodedPayload = Base64UrlEncode (ConvertTo-Json $Payload -Compress)
+  $UnsignedToken = "$EncodedHeader.$EncodedPayload"
+
+  # === STEP 2: Sign the token using Azure CLI ===
+  $UnsignedTokenBytes = [System.Security.Cryptography.SHA256]::Create().ComputeHash([Text.Encoding]::ASCII.GetBytes($UnsignedToken))
+  $Base64Value = [Convert]::ToBase64String($UnsignedTokenBytes)
+
+  $SignResultJson = az keyvault key sign `
+      --vault-name $VaultName `
+      --name $KeyName `
+      --algorithm RS256 `
+      --digest $Base64Value | ConvertFrom-Json
+
+  $Signature = $SignResultJson.signature
+  return "$UnsignedToken.$Signature"
+}
+
+function Get-GitHubInstallationId {
+    param(
+        [Parameter(Mandatory)][string] $Jwt,
+        [Parameter(Mandatory)][string] $ApiBase,
+        [Parameter(Mandatory)][string] $ApiVersion,
+        [Parameter(Mandatory)][string] $InstallationTokenOwner
+    )
+
+    $headers = Get-Headers -Jwt $Jwt -ApiVersion $ApiVersion
+
+    $uri = "$ApiBase/app/installations"
+    $resp = Invoke-RestMethod -Method Get -Headers $headers -Uri $uri -TimeoutSec 30
+
+    $resp | Foreach-Object { Write-Host "  $($_.id): $($_.account.login) [$($_.target_type)]" }
+
+    $resp = $resp | Where-Object { $_.account.login -ieq $InstallationTokenOwner }
+    if (!$resp.id) { throw "No installations found for this App." }
+    return $resp.id
+}
+
+function New-GitHubInstallationToken {
+  param(
+    [Parameter(Mandatory)] [string] $Jwt,
+    [Parameter(Mandatory)] [string] $InstallationId,
+    [Parameter(Mandatory)] [string] $ApiBase,
+    [Parameter(Mandatory)] [string] $ApiVersion
+  )
+  $headers = Get-Headers -Jwt $Jwt -ApiVersion $ApiVersion
+  $uri = "$ApiBase/app/installations/$InstallationId/access_tokens"
+  $resp = Invoke-RestMethod -Method Post -Headers $headers -Uri $uri -TimeoutSec 30
+  if (!$resp.token) { throw "Failed to obtain installation access token for installation $InstallationId." }
+  return $resp.token
+}
+
+Write-Host "Generating GitHub App JWT by signing via Azure Key Vault (no key export)..."
+$jwt = New-GitHubAppJwt -VaultName $KeyVaultName -KeyName $KeyName -AppId $GitHubAppId
+
+Write-Host "Fetching installation ID for $InstallationTokenOwner ..."
+$installationId = Get-GitHubInstallationId -Jwt $jwt -ApiBase $GitHubApiBaseUrl -ApiVersion $GitHubApiVersion -InstallationTokenOwner $InstallationTokenOwner
+
+Write-Host "Installation ID resolved: $installationId"
+
+Write-Host "Exchanging JWT for installation access token..."
+$installationToken = New-GitHubInstallationToken -Jwt $jwt -InstallationId $installationId -ApiBase $GitHubApiBaseUrl -ApiVersion $GitHubApiVersion
+
+# Export for gh CLI & git
+$env:GH_TOKEN = $installationToken
+Write-Host "GH_TOKEN has been set in the current process."
+
+# Optionally set an Azure DevOps secret variable (so later tasks can reuse it)
+if ($PipelineVariableName) {
+  Write-Host "##vso[task.setvariable variable=$PipelineVariableName;issecret=true]$installationToken"
+  Write-Host "Azure DevOps variable '$PipelineVariableName' has been set (secret)."
+}
+
+try {
+  Write-Host "`n--- gh auth status ---"
+  & gh auth status
+}
+catch {
+  Write-Warning "gh CLI not found or auth status failed: $($_.Exception.Message)"
+}