Fix "Error validating login to endpoint"

[forsyth2]

If zstash has a Error validating login to endpoint error, check that you're logged into the Globus endpoint:

1. Go to https://app.globus.org/file-manager?two_pane=true
2. For "Collection", choose the endpoint that ztsash is erroring because of.
3. If it says "Authentication required", you need to follow that process.