Support OIDC login from publisher CLI for subregistries

[elnaterator]

Is your feature request related to a problem? Please describe.

I am working on extending the official registry for use as an enterprise registry using a custom OIDC auth provider. I would like to be able to use the publisher CLI tool to publish internal MCP servers directly to the private registry. While the API supports custom OIDC providers, the publisher CLI does not currently. Since specifying a subregistry url is supported, it seems it should also support OIDC login which a subregistry may use.

Describe the solution you'd like

I would like to be able do the following:

mcp-publisher login oidc --registry https://private-mcp-registry.example.com

How it would work:

• If the registry API has OIDC auth enabled then the /v0/health endpoint would return the OIDC issuer and client id
• The publisher cli would use this info to initiate login via device auth flow, similar to github login

Although I could create our own customized publisher CLI, this seems like a generally useful feature for many private registries based on this project. Adding this to the main publisher CLI enables enterprises to just use the generally available publisher cli to publish to their own internal registries.

If this seems worthwhile I am happy to submit a PR for this feature.