Fixes #38424: correct response code of oauth2 token request to registry

[MartinSpiessl]

If oauth2 authentication (via POST request) is not supported, a container registry should respond with code 404, but we currently respond with 415 (Unsupported Media Type). By disabling the media type check for the token endpoint, we will return 401 (unauthorized) instead, which is enough for some clients to then try the regular token authentication. Adding a custom before_action, we can achieve that 404 is returned, thus we are fully compliant with the spec:
https://docker-docs.uclv.cu/registry/spec/auth/oauth/

What are the changes introduced in this pull request?

• content type check is disabled for :token
• POST requests on :token trigger a 404 response (the spec demands to return 404 if this is not supported)

Considerations taken when implementing this change?

• Adhere to the spec
• only disable media type check where necessary

What are the testing steps for this pull request?

The following curl request can be used to test the response (replace foreman.example.com with your foreman instance, orgname with your orgname, productname with your product name for the container registry, and containername is arbitrary, as is username and password):

curl -k -X POST "https://forman.example.com/v2/token" \
-H "Content-Type: application/x-www-form-urlencoded" \
--data-urlencode "scope=repository:orgname/productname/containername:pull,push repository:registry:pull,push" \
--data-urlencode "grant_type=password" --data-urlencode "username=myuser" \
--data-urlencode "password=mypassword" \
--data-urlencode "service=foreman.example.com" -w "\\n%{http_code}\\n"

This will yield the following output:

{
"error": {"message":"Media type in 'Content-Type: application/x-www-form-urlencoded' is unsupported in API v2 for POST and PUT requests. Please use 'Content-Type: application/json'."}
}


415

With the fix applied the output is simply:

404

Summary by Sourcery

Ensure compliance with OAuth2 spec by returning 404 for unsupported POST requests to the /v2/token endpoint.

Bug Fixes:

• Return 404 for POST requests to the OAuth2 token endpoint instead of 415 error when unsupported.

Enhancements:

• Add token_request_type_check before_action and skip media type validation for the token endpoint.

[sourcery-ai]

Reviewer's Guide

Disable media type validation and add a pre-filter on the token endpoint so that unsupported POST requests return 404, bringing OAuth2 token handling into spec compliance.

File-Level Changes

Change	Details	Files
Skip media type check on the :token action	Added :token to skip_before_action :check_media_type	app/controllers/katello/api/registry/registry_proxies_controller.rb
Introduce a custom before_action to return 404 for POST token requests	Registered token_request_type_check for :token token_request_type_check issues head :not_found and halts on POST	app/controllers/katello/api/registry/registry_proxies_controller.rb

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[sourcery-ai]

Hey @MartinSpiessl - I've reviewed your changes and they look great!

Here's what I looked at during the review

• 🟢 General issues: all looks good
• 🟢 Security: all looks good
• 🟢 Testing: all looks good
• 🟢 Documentation: all looks good

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[ianballou]

Thanks for the contribution @MartinSpiessl!

I believe there's a more straight-forward way to make POST requests return 404s via our registry:

katello/config/routes/api/registry.rb

Line 9 in fc2993d

match '/v2/token' => 'registry_proxies#token', :via => :post

If this line is removed, sending a POST to the token endpoint should result in a 404.

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However, this makes me wonder why we have defined a POST endpoint for tokens if it does not work. It looks like the endpoint fails because our API only expects JSON input, not application/x-www-form-urlencoded.

It looks like it was added 7 years ago: #7249
I suppose either the standard changed at some point, or perhaps even the POST route snuck in without proper testing.

It would be nice to get this endpoint to work properly -- we might not be far away from a working implementation. I won't make that a requirement of this PR though. I'll at least make sure a redmine gets filed for it depending on the outcome of this PR.

[ianballou]

To add to my review - is there a deeper end goal for some specific tool / client to work with our registry?

[nadjaheitmann]

@MartinSpiessl Do you mind coming back to this?

[MartinSpiessl]

@MartinSpiessl Do you mind coming back to this?

Yes, sorry, I will look at it today, I had a bit of a pile up of todos here recently

is there a deeper end goal for some specific tool / client to work with our registry?

For now the goal is to make it work with helm, where there are also other issues things I am currently investigating.

It would be nice to get this endpoint to work properly -- we might not be far away from a working implementation. I won't make that a requirement of this PR though. I'll at least make sure a redmine gets filed for it depending on the outcome of this PR.

Thanks! Yes it would be great to have that end point work, but for now I would focus on get the registry work for helm, and I would treat the POST endpoint as an orthogonal issue.

I believe there's a more straight-forward way to make POST requests return 404s via our registry:

Thanks, I will try that out and get back with an update to this PR.