The VK-only scaffolding had a shape problem worth fixing before anything
was built on it: completeCallback(code, codeVerifier) took the PKCE
verifier from the client, which forces the browser to generate and hold
it. We are a confidential client - a browser-held verifier buys nothing
and adds a place to steal it from.
Replaces the four vk-id-* files with a provider-agnostic surface:
getAuthorizeUrl(provider, returnTo?)
listIdentities()
unlink(provider)
completeCallback is gone entirely. The backend mints and stores state and
code_verifier single-use for 10 minutes, handles the provider's callback
itself, issues the session cookie and redirects. VK and Yandex differ
only in a path segment, because everything that actually differs between
them - PKCE handling, VK's device_id, Yandex's Basic-auth exchange -
lives backend-side.
vk-id-login becomes social-login-button with a provider input; adding
Yandex to the UI is an input value, not new code. Adds yandex_id to
ExternalIdentityProvider, plus optional email/phone/displayName since VK
frequently returns no email.
social-identity-gateway.spec.ts (5 tests) asserts the requests carry no
code_verifier and no client_secret, so reintroducing a browser-held
verifier fails the build rather than passing review.
PHASE-8 §2 rewritten to match: the four endpoints, backend-owned state
and verifier, UNIQUE (provider, providerUserId) with conflict routed to
controlled resolution rather than a silent rebind, per-tenant OAuth app
config under the Track S §4.2 envelope, and both providers' full endpoint
sets. Two things recorded there because they are expensive to discover
later: VK's callback returns device_id alongside code and the token
exchange fails without it, and both providers validate redirect_uri
against an exact registered list - which a multi-tenant platform cannot
satisfy without a central identity host (FH-0.1, still undecided).
256 tests pass. Build green, boundaries and cycles green.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
