Thursday 1 December 2022

Teams PowerShell Module - Certificate Authentication

There are several ways to get the Teams PowerShell module to authenticate against Azure in order to get access to running Teams PowerShell in your Tenancy. Most people will be used to using the interactive method, where you just run the basic Connect-MicrosoftTeams command and get an interactive Azure auth screen that pops up and you enter your user account details into. This is fine if you are manually connecting and doing this by hand. However, what if you want to run an Azure Function that needs to authenticate automatically each time it executes? Well, for that you want to use an application authentication method.

Currently as of the module version 4.9.1, Microsoft officially supports two methods for application authentication when connecting to the Teams PowerShell module:

  • Certificate based authentication – In this method you have a certificate with private and public keys. The PC connecting to Azure needs to have a copy of the private key and Azure needs to have a stored copy of the public key. As part of the connection the private key will be used to sign the connection and if Azure can decrypt the information with the public key then the PC is trusted to connect. This essentially makes the private key like a password that you need to ensure that no one else has access to.
  • Token based authentication – The token-based method requires that you set up a Client Secret in Azure. When you connect to Azure using the PowerShell module, you authenticate against the Token Service using the Client Secret and get Tokens back that you can use to connect to the service. In the case of the Teams module, you need to get two tokens to be able to run all the commands. You can find out more about this option here: Token Auth Post

In this post we are going to focus on the certificate-based authentication method. Here are the steps for setting up and connecting using certificate-based authentication:


Step 1: Generate a Certificate:

The good news here is that the certificate you need does not need to be signed by an internet-based Certificate Authority. You can simply create a self-signed certificate on a PC and use this for connection. Below is a PowerShell command you can run (you must run the PowerShell window as Administrator to execute it). The most important flag in the command is the KeySpec flag which tells it to generate a certificate that can be used for Key Exchange.

New-SelfSignedCertificate -certstorelocation cert:\localmachine\my -Subject TeamsAppTestCertificate01 -KeySpec KeyExchange


Step 2: Export the Certificate:

In order to export the certificate you can either run PowerShell or do it by hand with the Certificate Snap-in. Both options will be detailed below. Choose the one that you’re most comfortable with.

Export the Private Key (This step is only needed if you want to run PowerShell from a different machine that you have created the certificate on, for example, a Function App, etc):


$password = ConvertTo-SecureString -String "SpecialPassword123!" -Force –AsPlainText

Export-PfxCertificate -Cert "cert:\LocalMachine\My\8E4CKSHDUSG873F66D99AC7935F53" -FilePath "C:\temp\AuthPrivateKey.pfx" -Password $password

Note: The thumbprint to be used here will be output from the New-SelfSignedCertificate command you previously ran.


Or Windows UI:

Once again, this is is only needed if you want to run PowerShell from a different machine that you have created the certificate on, for example, a Function App, etc.

Search PC for mmc.exe > File Menu > Add or Remove Snap-in > Certificates > Add > Computer Account > Personal > Certificates Folder > Right Click on the Certificate > Export…

Export Certificate Wizard:

Click Next...

Select: "Yes, export the private key":

Go with the default export options:

Enter a password for the PFX file and ensure that you select TripleDES-SHA1 (I have found that importing on some platforms is not supported with AES):

Enter a name and location for the pfx file to be output to:

Export the Public Key (to be uploaded to the App Registration in Azure)


Export-Certificate -Cert "Cert:\LocalMachine\My\8E4CKSHDUSG873F66D99AC7935F53" -FilePath "C:\temp\AuthPublicKey.cer"

Or Windows UI:

Click Next... 

Do not export private key:

Select the format of the file (DER is okay in this case) and click next:

Select the name of the file and click next:

Step 3: Configure the App Registration:

Open the Azure AD Portal and select the Azure Active Directory > App Registration section:

 Click the "New Registration" Button:


Fill in a name for the application and click the Register button:

The App Registration will now be created, however, there is still more config to do:

Go to the “Certificates & secrets” blade:

Select the location of the public key certificate that you exported earlier. Add a description and click OK:

The certificate should now show up in the certificates area:

Now open the API Permissions tab within the App Registration, Click "Add a permission":

You will need to add the following Graph API permissions to the App Registration:








These permissions are documented by Microsoft here, so you may want to check to see if there have been any updates for the PowerShell version you're using:

Click the "Microsoft Graph" option:

Select "Application Permissions":

Select the permissions that were listed above:

Ensure that you have added all the permissions. If you missed any then repeat the above steps for all the permissions in the list…


After adding all the permissions, you need to click the “Grant admin consent for <tenant id>” button on the main Permissions screen:

At the end of this procedure, you should have the following permissions all assigned with admin consent granted:

In a final twist in this adventure, you also need to make sure you assign Teams Administrator privileges to the App Registration in order for it to be able to run CS commands. You do this by going to the Active Directory tab > Roles and Administrators > Teams Administrator Role:


Assign the Service Permission that is named the same as your App Registration to the RBAC Role:

Connecting To Teams PowerShell


Now that all the backend work has been done we can get down to doing some connecting. When you connect it needs to be from a machine that has access to the certificate. On a PC this means it has to be in the certificate store. If it’s from a machine in Azure there are various methods for doing this too (which I may well get to in another post…).

You will need to know the ApplicationId that was given to the App Registration in Azure. You can find this out by looking going to the Overview tab and looking for the GUID that has the title “Application (client) ID”. The TenantId is the base domain name that was first given to your tenancy when it was created or alternatively can be the GUID that’s in the Overview tab named as “Directory (tenant) ID” (both options will work).


Teams Module Connect Command:

Connect-MicrosoftTeams -CertificateThumbprint "3ab0e057bc3278ecb2a33123042e5a7a8001ff8c" -ApplicationId "319d0a47-9a48-45b0-b416-14aca00e7ece" -TenantId


When connection is successful, you’ll get back an object displayed in the PowerShell window that tells you the Account, Environment, Tenant and TenantId values. From here you should be able to run almost all of the commands from the module, with the following exclusions:

As of 4.9.1; All cmdlets are supported now, except for the cmdlets mentioned below:

  • New-Team
  • [Get|Set|New|Sync]-CsOnlineApplicationInstance
  • *-CsUserCallingSettings
  • *-CsUserCallingDelegate
  • *PolicyPackage*
  • *-CsTeamsShiftsConnection*
  • *-CsBatchTeamsDeployment*


The Wrap Up


Congratulations, you’re now an expert at certificate-based authentication with the Teams PowerShell module. If you are interested in Token Based Authentication using the Teams Module, then you can check out my post on that over here: Token Auth Post.

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