Build the GitHub button's URL in Go, not in four templates

[compscidr]

Follow-up to #638, prompted by a fair observation: it is odd that the themes carry this logic.

The leftover

#631 moved GitHub's authorize URL into Go so the escaping was decided once. It left each theme assembling the URL that reaches it:

<a id="github-button" href="/login/github{{ if .next }}{{ if ne .next "/" }}?next={{ .next | urlquery }}{{ end }}{{ end }}">

A nested conditional building a URL, copied into four repositories — the same shape of problem the earlier work set out to remove, one step further out.

The change

GithubLoginURL decides it, and the templates print the result:

<a id="github-button" href="{{ .github_login_url }}">

Beyond being shorter, this makes the URL's shape the server's business: if it ever needs another parameter, no theme changes again.

next stays in the context because the email login still redirects to it in the browser once its AJAX call succeeds — behaviour rather than URL construction.

Tests

• TestGithubLoginURL — the empty and / cases give a bare path; & in next is escaped rather than starting a second parameter
• TestGithubLoginURL_SurvivesARoundTrip — what the button points at parses back to the next it was built from, since GithubLogin reads it as a query parameter

Verified against a local instance

/login request	rendered href
no next	/login/github
?next=/admin/settings	/login/github?next=%2Fadmin%2Fsettings
?next=https://evil.example	/login/github (dropped by SafeNext)

Then followed it through: the button's URL redirects to GitHub with a state, and replaying GitHub's return with that state reaches the exchange — so the stored next and state still round-trip.

Themes

• Print the GitHub button's URL instead of assembling it goblog-site-theme#13
• Print the GitHub button's URL instead of assembling it goblog-theme-forest#7
• Link to /login/github instead of building the OAuth URL here goblog-theme-minimal#4 (still open from the last round, so it absorbs this rather than needing its own)

Merge order as before: this first, then the themes. An un-updated theme renders an empty href on the button, so unlike the last round they do want updating promptly — but nothing else on the page is affected.

🤖 Generated with Claude Code

[Copilot]

Copilot review overview

🟢 Approval recommended

The change cleanly centralizes URL construction server-side, updates the affected template, and adds targeted tests that validate both escaping and round-trip behavior.

Review effort: Lite
Findings: None

What changed in this PR

Moves construction of the /login/github button URL out of theme markup and into Go so URL shape/escaping is defined once server-side, with coverage to ensure next is correctly preserved and safely encoded.

Changes:

• Add GithubLoginURL(next) helper to build /login/github (optionally with ?next=...) using consistent escaping rules.
• Pass github_login_url into the login template context and simplify the template to render it directly.
• Add unit tests covering empty// cases, escaping (including &), and round-trip parsing of next.

File	Description
themes/​default/​templates/​login.html	Replaces inline conditional URL-building with {{ .github_login_url }}.
blog/​blog.go	Introduces GithubLoginURL, computes next once, and injects github_login_url into the render context.
blog/​github_login_test.go	Adds tests to validate escaping behavior and round-trip parsing for the constructed login URL.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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