Verification is the whole endpoint

[authenticate_bearer] runs signature, iss, exp, aud, token_use, the closed trusted-issuer set, the org-header match and the #317 session-revocation check, with require_cognito — you exchange an identity-provider session for our cookies, never a self-issued OAuth token. Without it this endpoint would set a session cookie from an attacker-chosen string.

require_acting_team is false: the client learns its teams from this response, so demanding an acting team to sign in is unsatisfiable. Same arm GET /users/me takes.

⚠️ Login CSRF / session fixation, and the four things that stop it

The attack is forcing a victim's browser to POST an attacker's tokens here, so the victim then works inside the attacker's session — for a log product, the victim's queries landing in the attacker's org with the audit trail naming the attacker's user. Four controls block it, and the first two are the ones a refactor could quietly remove:

1. Json refuses a cross-site form post. An HTML <form> can only send application/x-www-form-urlencoded, multipart/form-data or text/plain; axum's Json extractor answers 415 to all three. Accepting form encoding here — or hand-parsing the body — deletes this defence. a_form_encodable_post_is_refused is the guard;
2. the API has no CORS layer, so a cross-origin fetch(..., {credentials: 'include'}) fails CORS and the browser discards this response's Set-Cookie (rh-jculnc);
3. the CSRF layer refuses this route like any other — rh-cl95c's predicate keys on Sec-Fetch-Site, not on a session cookie, precisely so it covers the route that creates the session (a cookie-gated check could not, by construction);
4. __Host- means only script on the victim's own origin could plant a cookie directly, which is already game over for other reasons.

Response Body

curl -X POST "https://example.com/auth/session" \  -H "Content-Type: application/json" \  -d '{    "access_token": "string",    "refresh_token": "string"  }'

{  "organization_slug": "string",  "user": {    "avatar": "string",    "created_at": "string",    "email": "string",    "id": "string",    "is_admin": true,    "kind": "native",    "last_login_at": "string",    "name": "string",    "org_id": "string",    "provisioned_by": "string",    "role": null,    "status": null,    "status_unrecognized": "string",    "team_ids": [      "string"    ],    "updated_at": "string"  }}