PVCs fail to be created if a username does not begin with a "safe" character

[m-bull]

Bug description

PVCs fail to be created if a username does not begin with a "safe" character (set(string.ascii_lowercase + string.digits)).

If a username begins with a "non-safe" character, when it is url-encoded here, it may end up beginning with a -.

This is subsequently included as a PVC label value, which is not allowed.

Expected behaviour

PVC creates successfully even if usernames begin with "unsafe" characters.

Actual behaviour

PVC fails to create with the following message:

HTTP response body: {"kind":"Status","apiVersion":"v1","metadata":{},"status":"Failure","message":"PersistentVolumeClaim \"claim--53cott-40stackhpc-2ecom\" is invalid: metadata.labels: Invalid value: \"-53cott-40stackhpc-2ecom\": a valid label must be an empty string or consist of alphanumeric characters, '-', '_' or '.', and must start and end with an alphanumeric character (e.g. 'MyValue',  or 'my_value',  or '12345', regex used for validation is '(([A-Za-z0-9][-A-Za-z0-9_.]*)?[A-Za-z0-9])?')","reason":"Invalid","details":{"name":"claim--53cott-40stackhpc-2ecom","kind":"PersistentVolumeClaim","causes":[{"reason":"FieldValueInvalid","message":"Invalid value: \"-53cott-40stackhpc-2ecom\": a valid label must be an empty string or consist of alphanumeric characters, '-', '_' or '.', and must start and end with an alphanumeric character (e.g. 'MyValue',  or 'my_value',  or '12345', regex used for validation is '(([A-Za-z0-9][-A-Za-z0-9_.]*)?[A-Za-z0-9])?')","field":"metadata.labels"}]},"code":422}

How to reproduce

Spawn a singleuser notebook with an attached PVC and a username that begins with an uppercase letter.

Your personal set up

  - name: jupyterhub
    version: 2.0.0
    repository: https://jupyterhub.github.io/helm-chart/

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[manics]

This is a known issue, please follow https://github.com/jupyterhub/kubespawner/issues/498