Authenticate via OAuth with App Secret to EWS in PowerShell

Question

I am seeking the proper PowerShell code for how to authenticate to EWS via OAuth with only an app secret instead of a username and password. I have the app registration set with full_access_as_app permissions. The use case is the application runs is a daemon that sends emails based on supplied to and from addresses. The from users are remote users do not authenticate into the system so process that handles sending the emails cannot authenticate as them via OAuth.

I found this it was helpful so I assume only the part about getting the token needs to be changed: Powershell, EWS, OAuth2, and automation

Answer 1

There are a few different approaches you could take eg if you used the MSAL library which is different from ADAL which the script you pointed is using then you could do something like.

$ClientId = "9d5d77a6-xxxx-473e-8931-958f15f1a96b"
$MailboxName = "gscales@domain.com"
$RedirectUri = "msal9d5d77a6-fe09-473e-8931-958f15f1a96b://auth"
$ClientSecret = "xxx";
$Scope = "https://outlook.office365.com/.default"
$TenantId = (Invoke-WebRequest https://login.windows.net/datarumble.com/v2.0/.well-known/openid-configuration | ConvertFrom-Json).token_endpoint.Split('/')[3]
$app =  [Microsoft.Identity.Client.ConfidentialClientApplicationBuilder]::Create($ClientId).WithClientSecret($ClientSecret).WithTenantId($TenantId).WithRedirectUri($RedirectUri).Build()
$Scopes = New-Object System.Collections.Generic.List[string]
$Scopes.Add($Scope)
$TokenResult = $app.AcquireTokenForClient($Scopes).ExecuteAsync().Result;