az acr login failure

Attempting to log in to a Container Registry server gives me a “stub received bad data” error. (Same thing happens running PowerShell in admin mode.)

PS> az acr login --name contregdmsmith
Error saving credentials: error storing credentials - err: exit status 1, out: `The stub received bad data.

### Environment summary

Install Method: MSI
CLI version: azure-cli (2.0.20)
OS version: Windows 10 (1703 // 15063.674)
Shell Type: Powershell  

[yugangw-msft]

This is a known issue, see below for the workaround that @djyou provided through a recent email exchange

“acr login” uses AAD and docker in Windows uses wincred to save ACR refresh token by default. The token can sometimes exceed 4K in length (e.g., due to customized roles) which will get truncated. You didn’t see it when credential is specified because username/password pair is much shorter.

One quick workaround is to modify <User folder>\.docker\config.json file. Remove the following line so docker will use file system to store tokens:

               "credsStore": "wincred"

We are also rolling out a fix in the token server that will limit the token length.

[sajayantony]

@jblackburn21 - the Credential helper is something that is being worked on and not yet released. @shhsu is working on release it officially since this solves the credential renew issue. The main issue is that the token is larger than what windows credential store can handle and hence failing. The workaround that @djyou suggested is something that can unblock you and will create a config file that will use the default file credential store instead of the windows credential store.

'{"auths": {"contregdmsmith.azurecr.io": {}}}' | Set-Content $HOME/.docker/config.json
az acr login -n contregdmsmith

I think we can consider fixing the CLI to prompt setting the credential store automatically as a fix to this bug.