Vikunja's built-in OAuth server (Vikunja 2.3+) does not require client
registration and accepts arbitrary client_ids — it just enforces PKCE
(S256) and constrains redirect URIs to the vikunja- scheme. Earlier I
deferred OAuth on the assumption it needed a registered client; that
was wrong, and the docs make the path much smoother than POST /login.
The custom-scheme constraint (no http:// loopback) is side-stepped by
manual paste-back: veans prints the authorize URL, the user signs in,
their browser fails to open vikunja-veans-cli://callback?code=... and
shows an error, the user copies the URL from the address bar and
pastes it back. CLI extracts code + state, verifies state for CSRF,
exchanges via POST /api/v1/oauth/token (JSON body — Vikunja rejects
form-encoded), and returns the access token.
Resolution order in AcquireHumanToken:
1. --token (paste-in JWT or personal API token; SSO/OIDC users)
2. --use-password / --username + --password (POST /login)
3. OAuth flow (interactive default)
login command supports the same --use-password / --token escape hatches
for token rotation on instances with OAuth disabled.
Includes unit tests for the PKCE generator (verifier shape per RFC 7636,
challenge = SHA256(verifier) base64url-no-pad), authorize-URL
construction, and the lenient callback parser (full URL / query-only /
bare code).
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