Error: The Admin Username specified is not allowed

[gminog]

I have followed the instructions on getting the tenant Id, client Id and client secret using Azure CLI and I have adjusted my Vagrantfile accordingly.
However, when executing vagrant up --provider=azure --debug I'm getting an error similar to the below:
The Admin Username specified is not allowed. Code: Invalid Parameter, Target: adminUsername

The wizard that sets up the VM does not prompt for a username or something, so that's a pretty unexpected error message.
Any ideas?

[sonnysideup]

Check this issue: Azure/azure-cli#582

[boldandbusted]

Figuring this one out took me a bit, but I'm an Azure noob. :) It would have been nice to have Terraform fail on the plan and not the apply, and refer to a doc that details what is acceptable username formats and strings for SSH in Azure.