To set up peering between your classic and resource manager based virtual networks, log in to the Azure Management portal and select More Services from the left hand menu. Select Virtual Networks.
Once in Virtual Networks, find a network that is in the same region, and uses the same subscription as the one selected for Azure Active Directory (if you have more than one). Ideally, you will have created the network you planned on using already, but if not, it is possible to create one first, then follow these steps. In this case, we used a classic network based in the North Europe region, and a specific Pay-as-You-Go subscription. We will select one with these same properties.
Once selected, find Peerings in the selected Virtual Network's menu. Click Add.
Next, provide a name for the Peering (1). As we are trying to ensure Azure AD connectivity to Resource Manager resources, it will be a Resource Manager deployment model. This is the default setting. Select the subscription that the classic virtual network was created with, and select the virtual network (3). In this case we have a peering created already, but as you can see, a peering can be created on any of the networks with the selected subscription and location (4). Finally, you can configure access (5), and optional settings (6). Click OK when you are finished and your peering will be created (7).
Once peering has been established, you can begin to configure SoftNAS instances to join the created Azure Active directory, using the SoftNAS AD Wizard, as per the instructions provided in Active Directory Configuration.