internal/oauth: assorted fixes and cleanups

[thaJeztah]

• slightly related to internal/oauth: use BROWSER env var to open the login URL #7409

internal/oauth: avoid opening browser after login cancellation

Check the context after reading stdin to avoid launching the browser
if login was canceled while waiting for ENTER.

internal/oauth: combine "web-based login" message with info note

Make the output less verbose, and combine the "web-based login" message
with the info message that's already printed.

Before this patch:

docker login

USING WEB-BASED LOGIN

i Info → To sign in with credentials on the command line, use 'docker login -u <username>'

Your one-time device confirmation code is: VVPV-NSSL
Press ENTER to open your browser or submit your device code here: https://login.docker.com/activate

Waiting for authentication in the browser…

With this patch:

docker login

i Info → Using web-based login. To sign in with credentials on the command line, use 'docker login -u <username>'

Your one-time device confirmation code is: QBBD-PQNS
Press ENTER to open your browser or submit your device code here: https://login.docker.com/activate

Waiting for authentication in the browser…

internal/oauth: handle error when failing to open browser

Before this patch, pressing ENTER to open the browser would silently
discard the error;

docker login

i Info → Using web-based login. To sign in with credentials on the command line, use 'docker login -u <username>'

Your one-time device confirmation code is: VGTB-VKBG
Press ENTER to open your browser or submit your device code here: https://login.docker.com/activate

Waiting for authentication in the browser…

With this patch, a failure is printed, so that the user can manually open
the URL (or cancel the login);

docker login

i Info → Using web-based login. To sign in with credentials on the command line, use 'docker login -u <username>'

Your one-time device confirmation code is: SZFX-BSGP
Press ENTER to open your browser or submit your device code here: https://login.docker.com/activate

Waiting for authentication in the browser…

No browser found. Open the URL above manually to continue.

internal/oauth: cleanup output

• Remove extra newline before message
• Include the token in the URL (instead of requiring the user to manually
  enter it on the website).
• Improve the "call to action"; ENTER can be used to automatically open
  the browser (but the user can manually open it instead), and CTRL-C can
  be used to cancel the login.
• Remove the "Waiting for authentication in the browser…" message, which
  could be confusing if no browser was opened (yet), instead print a message
  after successfully requesting the browser to be opened.

When running docker login;

docker login

i Info → Using web-based login. To sign in with credentials on the command line, use 'docker login -u <username>'

Your one-time device confirmation code is: NRJL-BLRL
Open this URL to authenticate: https://login.docker.com/activate?user_code=NRJL-BLRL

Press ENTER to open the URL in your browser, or Ctrl+C to cancel.

After pressing ENTER, it either prints the "success" message;

Press ENTER to open the URL in your browser, or Ctrl+C to cancel.

Opening browser…

or a failure when unable to launch a browser;

Press ENTER to open the URL in your browser, or Ctrl+C to cancel.

No browser found. Open the URL above manually to continue.

internal/oauth: remove debug logs, and move them to the caller

Wrap errors in the OAuth manager instead of logging them, preserving
the underlying cause while allowing callers to detect startup failures.

Log failures at the fallback handler and scope the device-code login
result to its branch.

Release notes (optional)

A picture of a cute animal (not mandatory but encouraged)

[codecov-commenter]

Codecov Report

❌ Patch coverage is 36.00000% with 16 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
internal/oauth/manager/manager.go	38.09%	13 Missing ⚠️
cli/command/registry/login.go	25.00%	3 Missing ⚠️

📢 Thoughts on this report? Let us know!

[docker-agent]

Assessment: 🟢 APPROVE

[docker-agent]

Assessment: 🟢 APPROVE

[docker-agent]

Assessment: 🟢 APPROVE