PowerShell Function to get Microsoft Graph API token using your app's client ID, client Secret and Tenant Domain

Office365TokenGet.psm1

Function New-MSGraphAPIToken {
    <# 
 
    .SYNOPSIS 
    Acquire authentication token for MS Graph API 
     
    .DESCRIPTION 
    If you have a registered app in Azure AD, this function can help you get the authentication token 
    from the MS Graph API endpoint. Each token is valid for 60 minutes. 
     
    .PARAMETER appID 
    This is the registered appID in AzureAD 
     
    .PARAMETER appKey 
    This is the key of the registered app in AzureAD 
     
    .PARAMETER domain 
    This is your Office 365 Tenant Domain 
     
    .EXAMPLE 
    $graphToken = New-MSGraphAPIToken -appID <appID> -appKey <appKey> -domain <tenant domain> 
 
    The above example gets a new token using the appID, appKey and tenant domain combination 
     
    .NOTES 
    General notes 
    #>
    
    param(
    [parameter(mandatory=$true)]
    [string]$appID,
    [parameter(mandatory=$true)]
    [string]$appKey,
    [parameter(mandatory=$true)]
    [string]$domain
    )
    
    $body = @{grant_type="client_credentials";scope="https://graph.microsoft.com/.default";client_id=$appID;client_secret=$appKey}
    $oauth = Invoke-RestMethod -Method Post -Uri https://login.microsoftonline.com/$domain/oauth2/v2.0/token -Body $body
    $token = @{'Authorization'="$($oauth.token_type) $($oauth.access_token)"}    
    Return $token
}

Function New-OutlookRestAPIToken {
    <# 
    .SYNOPSIS 
    Acquire authentication token for Outlook REST API 
     
    .DESCRIPTION 
    If you have a registered app in Azure AD, this function can help you get the authentication token 
    from the Outlook REST API endpoint. Each token is valid for 60 minutes. 
     
    .PARAMETER appID 
    This is the registered appID in AzureAD 
     
    .PARAMETER appKey 
    This is the key of the registered app in AzureAD 
     
    .PARAMETER domain 
    This is your Office 365 Tenant Domain 
     
    .EXAMPLE 
    $graphToken = New-OutlookRestAPIToken -appID <appID> -appKey <appKey> -domain <tenant domain> 
 
    The above example gets a new token using the appID, appKey and tenant domain combination 
     
    .NOTES 
    General notes 
    #>
    param(
    [parameter(mandatory=$true)]
    [string]$appID,
    [parameter(mandatory=$true)]
    [string]$appKey,
    [parameter(mandatory=$true)]
    [string]$domain
    )
    
    $body = @{grant_type="client_credentials";scope="https://outlook.office.com/.default";client_id=$appID;client_secret=$appKey}
    $oauth = Invoke-RestMethod -Method Post -Uri https://login.microsoftonline.com/$domain/oauth2/v2.0/token -Body $body
    $token = @{'Authorization'="$($oauth.token_type) $($oauth.access_token)"}    
    Return $token
}