Beefing up ModernPOS security with a real app package signing certificate and AAD authentication

Overview

A real certificate should be used to code sign the ModernPOS packages. That will allow for more security and simpler deployments (as no self-signed certs will need to be installed before installing MPOS).

Since the real certificate is usually not accessible by all developers in the team (and should not be), non-official builds will keep using a simple self-signed cert, i.e. the Contoso certificate shipped with the Retail Sdk.

Additionally, recent releases of MPOS, RetailServer, and Dynamics AX use AAD app ids for proper authorization. A onetime setup in AAD and AX is needed. With the proper setup, we configure AX to only allow access from ModernPOS clients that claim the correct app id combination.

Note, that there is a direct relation between the signing certificate, the reply address of the final built ModernPOS and the AAD app id.

With these recent changes, non-production environments can be configured to allow both the real and self-signed ModernPOS clients to access. However, the actual production environment should only allow access by MPOS clients with real certs and self-signed certs should not be allowed.

An automatic benefit of this is that it cannot happen, that a developer connects by accident to production during development phase.

Note, that all the steps below have to be carried out once per tenant, and not per environment.

Detailed steps

Ideally, the following steps should be carried out after a dev environment is fully working with a self-signed cert. That ensures that AX is correctly setup (workers, stores, registers, etc.).

1. Build server setup

The first step is to install a real certificate on the build server so that the Retail Sdk build can use it.

Note, that the steps below require administrative access to the build server. Therefore a cloud-hosted build server is required (as opposed to a Microsoft-hosted build server without administrative privileges is not possible to be used).  This is unfortunate, and Microsoft is working on a solution.

  • 2. Initial Retail Sdk setup

    We want to use the certificate in Release builds (official) but keep using the Contoso signing cert for dev purposes in Debug builds. Other strategies can be used, but using the build flavor has worked well for some. The RetailSdk allows us to provide either a path to a certificate or a certificate thumbprint. We will use the first approach for the self-signed test certificate and the 2nd approach for the real certificate. We can use simple MSbuild logic to switch between the two. Below is an example how to do that. This change would have to be made to the RetailSdk’s customization.settings or better, to a global.props file sitting next to it with all customer values. Use the thumbprint from the step above.

    <!– Release builds pick up the secure cert from the build server with named thumbprint, Debug builds use the test cert part of the Retail Sdk –>
    <ModernPOSPackageCertificateKeyFile Condition=”‘$(ModernPOSPackageCertificateKeyFile)’ == ” and ‘$(Configuration)’ != ‘Release'”>$(MSBuildThisFileDirectory)\ModernPOSAppxSigningCert-Contoso.pfx</ModernPOSPackageCertificateKeyFile>
    <ModernPOSPackageCertificateThumbprint Condition=”‘$(ModernPOSPackageCertificateThumbprint)’ == ” and ‘$(Configuration)’ == ‘Release'”>22aa3bdca99b70d4ca44d0c51d23a07e06fcfc61</ModernPOSPackageCertificateThumbprint>

  • 3. AAD setup

    Carry out an official build in order to get a properly signed ModernPOS appx/installer
    Install the fully signed ModernPOS on a client machine and point to a RetailServer/AX environment of your choice (dev environment, for example)
    follow the steps in this blog to create 2 app ids: https://community.dynamics.com/ax/b/axforretail/archive/2017/11/05/mpos-aad-changes-in-monthly-update-4
    Activate ModernPOS

    4. Final Retail Sdk setup

    The final changes to the dllhost.exe.config you had to make in step 3 should be added to the RetailSdk\Assets\dllhost.exe.config file. That way, any new and officially build ModernPOS will automatically have the right app id information configured.
    Note: For development purposes, the older app id information must be used. This can be easily done by leaving the original settings in the config file, but leave them commented out. Switching between the production and dev ModernPOS is that as easy as un-commenting the developer values before activating MPOS.

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