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Obtain the access token from a Microsoft Azure Access Control Service (ACS) account that is associated with the customer's Microsoft Office 365 tenancy
<#
.Synopsis
Obtain an app-only access token from ACS.
.DESCRIPTION
Retrieves an app-only access token from ACS to call the specified principal
at the specified targetHost. The targetHost must be registered for target principal. If specified realm is
null, the "Realm" setting in web.config will be used instead
.EXAMPLE
Get-SPOAccessToken -Url "https://contoso.sharepoint.com/_api/web" -ClientId "" -ClientSecret ""
#>
Function Get-SPOAccessToken([string]$ClientId,[string]$ClientSecret,[Uri]$WebUri){
$SharePointPrincipal = "00000003-0000-0ff1-ce00-000000000000"
$realm = GetRealmFromTargetUrl -TargetApplicationUri $WebUri
$accessToken = GetAppOnlyAccessToken -ClientId $ClientId -ClientSecret $ClientSecret -TargetPrincipalName $SharePointPrincipal -TargetHost $WebUri.Authority -TargetRealm $realm
return $accessToken.access_token
}
function GetRealmFromTargetUrl([Uri]$TargetApplicationUri)
{
$url = $WebUrl + "/_vti_bin/client.svc"
$headers = @{}
$headers.Add('Authorization','Bearer')
try {
$response = Invoke-WebRequest -Uri $TargetApplicationUri -Headers $headers -Method Get
}
catch [Net.WebException] {
$authResponseHeader = $_.Exception.Response.Headers["WWW-Authenticate"]
#$bearerKey = "Bearer realm="
$bearer = $authResponseHeader.Split(",")[0]
$targetRealm = $bearer.Split("=")[1]
return $targetRealm.Substring(1,$targetRealm.Length-2)
}
return $null
}
Function GetAppOnlyAccessToken([string]$ClientId,[string]$ClientSecret,[string]$TargetPrincipalName,[string]$TargetHost,[string]$TargetRealm)
{
$resource = GetFormattedPrincipal -PrincipalName $TargetPrincipalName -HostName $TargetHost -Realm $TargetRealm
$ClientId = GetFormattedPrincipal -PrincipalName $ClientId -Realm $TargetRealm
$contentType = 'application/x-www-form-urlencoded'
$stsUrl = GetSecurityTokenServiceUrl -Realm $TargetRealm
$oauth2Request = CreateAccessTokenRequestWithClientCredentials -ClientId $ClientId -ClientSecret $ClientSecret -Scope $resource
$oauth2Response = Invoke-RestMethod -Method Post -Uri $stsUrl -ContentType $contentType -Body $oauth2Request
return $oauth2Response
}
Function GetSecurityTokenServiceUrl([string]$Realm)
{
return "https://accounts.accesscontrol.windows.net/$Realm/tokens/OAuth/2"
}
Function CreateAccessTokenRequestWithClientCredentials([string]$ClientId,[string]$ClientSecret,[string]$Scope)
{
$oauth2Request = @{
'grant_type' = 'client_credentials';
'client_id' = $ClientId;
'client_secret' = $ClientSecret;
'scope' = $Scope;
'resource' = $Scope
}
return $oauth2Request
}
function GetFormattedPrincipal([string]$PrincipalName, [string]$HostName, [string]$Realm)
{
if ($HostName)
{
return "$PrincipalName/$HostName@$Realm"
}
return "$PrincipalName@$Realm"
}
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