Get ms alias from github identity.

eng/common/scripts/Get-AADIdentityFromGithubUser.ps1

@@ -0,0 +1,77 @@
+<#
+.DESCRIPTION
+Get the corresponding ms alias from github identity
+.PARAMETER AadToken
+The aad access token.
+.PARAMETER GithubName
+Github identity. E.g sima-zhu
+.PARAMETER ContentType
+Content type of http requests.
+.PARAMETER AdditionalHeaders
+Additional parameters for http request headers in key-value pair format, e.g. @{ key1 = val1; key2 = val2; key3 = val3}
+#>
+[CmdletBinding(SupportsShouldProcess = $true)]
+param(
+  [Parameter(Mandatory = $true)]
+  [string]$TenantId,
+
+  [Parameter(Mandatory = $true)]
+  [string]$ClientId,
+
+  [Parameter(Mandatory = $true)]
+  [string]$ClientSecret,
+
+  [Parameter(Mandatory = $true)]
+  [string]$GithubUser
+)
+. "${PSScriptRoot}\logging.ps1"
+
+$OpensourceAPIBaseURI = "https://repos.opensource.microsoft.com/api/people/links/github/$GithubUser"
+
+function Generate-AadToken ($TenantId, $ClientId, $ClientSecret) {
+    $LoginAPIBaseURI = "https://login.microsoftonline.com/$TenantId/oauth2/token"
+    try {
+        $headers = @{
+            "content-type" = "application/x-www-form-urlencoded"
+        }
+
+        $body = @{
+            "grant_type" = "client_credentials"
+            "client_id" = $ClientId
+            "client_secret" = $ClientSecret
+            "resource" = "api://repos.opensource.microsoft.com/audience/7e04aa67"
+        }
+        Write-Host "Generating aad token..."
+        $resp = Invoke-RestMethod $LoginAPIBaseURI -Method 'POST' -Headers $headers -Body $body
+    }
+    catch { 
+        LogError $_
+        exit 1
+    }
+
+    return $resp.access_token
+} 
+
+$Headers = @{
+    "Content-Type" = "application/json"
+    "api-version" = "2019-10-01"
+}
+
+try {
+    $opsAuthToken = Generate-AadToken -TenantId $TenantId -ClientId $ClientId -ClientSecret $ClientSecret
+    $Headers["Authorization"] = "Bearer $opsAuthToken"
+    Write-Host "Fetching aad identity for github user: $GithubName"
+    $resp = Invoke-RestMethod $OpensourceAPIBaseURI -Method 'GET' -Headers $Headers
+}
+catch { 
+    LogError $_
+    exit 1
+}
+
+$resp | Write-Verbose
+
+if ($resp.aad) {
+    return $resp.aad.alias
+}
+
+LogError "Failed to retrieve the aad identity from given github user: $GithubName"