PUT /api/groups/{gid}/members/{pid}

Add a principal to a group. Idempotent.

Adds {pid} to group {gid} and verifies by a fresh membership read -- a SEPARATE operation, because the receipt the add resolves merely ECHOES the ids that were sent.

The request is idempotent: the path names the exact membership, so re-sending it leaves the same membership.

Authentication

Send the session id as Authorization: Bearer <session id>, and an RFC 9449 DPoP proof in the DPoP header if your session is bound to a key. The two are required together, not as alternatives — see Authenticating and Proving you hold your key.

This surface sets no cookie

There is no session cookie on any response and none is read on any request. Do not set credentials: "include" on a browser fetch.

Parameters

Name	In	Required	Type	Description
gid	path	yes	string	A group's principal id as 16 hex digits (the id field, not principalId).
pid	path	yes	string	The member principal's id as 16 hex digits (the id field, not principalId).

Request

No request body.

Responses

200

The principal is a member, verified by a fresh read.

Field	Type	Required	Description
code	string	no	Absent on success; NOT_SAVED when the read-back disagrees.
gid	string	no
pid	string	no
saved	boolean	no
count	integer	no
members	array of Principal	no	The membership as a FRESH read shows it -- a separate operation from the write.
detail	string	no

Example

{
  "code": "...",
  "gid": "...",
  "pid": "...",
  "saved": true,
  "count": 0,
  "members": [
    {
      "id": "...",
      "principalId": "...",
      "systemId": 0,
      "className": "...",
      "name": "...",
      "disabled": true,
      "roleIds": [
        "..."
      ],
      "groupIds": [
        "..."
      ]
    }
  ],
  "detail": "..."
}

400

BAD_REQUEST -- gid or pid is not 16 hex digits.

401

No live session, or a DPoP proof that did not verify.

SESSION_NOT_FOUND -- the credential names no session this Gateway holds. SESSION_EXPIRED -- it aged out. Both carry reauth: true; obtain a new credential rather than retrying.

PROOF_* -- the sender constraint refused. See the DPoP section of this document for the full table; PROOF_MALFORMED is a 400 and PROOF_REPLAY_CACHE_FULL a 503, and the rest are here.

SCOPED_CREDENTIAL_EXPIRED -- a scoped browser credential passed its fixed lifetime. Use does not extend it: an idle timeout would be refreshed by exactly the traffic a stolen handle produces.

403

Authenticated, and refused. The codes differ in what they say about where the refusal came from: ACCESS_DENIED and PRINCIPAL_DISABLED are the key server's, while NOT_WRITABLE, BUILT_IN_PRINCIPAL, OWN_ACCOUNT and OBJECT_NOT_IN_CREDENTIAL_SCOPE are decided by the Gateway before anything is sent.

404

NO_GROUP, NOT_A_GROUP, or NO_PRINCIPAL -- no principal {pid}. Nothing was written.

409

CYCLIC_MEMBERSHIP -- the key server refused because this edge would close a loop in group membership. Nothing was written. It is almost always the reverse membership: the group is already reachable as a member of the principal you are adding. This route does not walk the membership graph and cannot tell you which edge closed the loop.

NOT_SAVED -- the key server did not refuse and the membership read-back does not contain the principal.

500

A fault rather than a refusal.

OP_FAILED is the catch-all: the key server refused in words that match no classified pattern, so the Gateway cannot say more than that the operation did not happen. Some key server refusals that are conceptually a caller error arrive here rather than as a 4xx, because the wire carries no distinguishing code -- where a route can recognise one from its message it maps it, and each such mapping is documented on the operation.

503

A capacity ceiling or a missing deployment prerequisite. retryable says which.

A scope of session or process names the ceiling that was hit, and the response carries Retry-After.

Error handling

Every failure answers JSON carrying at least code and detail. Match on code — detail is written for a human debugging the call and its wording is not part of the contract. See the error model.

Status	Meaning
400	BAD_REQUEST -- gid or pid is not 16 hex digits.
401	No live session, or a DPoP proof that did not verify. SESSION_NOT_FOUND -- the credential names no session this Gateway holds. SESSION_EXPIRED -- it aged out. Both carry reauth: true; obtain a new credential rather than retrying. PROOF_* -- the sender constraint refused. See the DPoP section of this document for the full table; PROOF_MALFORMED is a 400 and PROOF_REPLAY_CACHE_FULL a 503, and the rest are here. SCOPED_CREDENTIAL_EXPIRED -- a scoped browser credential passed its fixed lifetime. Use does not extend it: an idle timeout would be refreshed by exactly the traffic a stolen handle produces.
403	Authenticated, and refused. The codes differ in what they say about where the refusal came from: ACCESS_DENIED and PRINCIPAL_DISABLED are the key server's, while NOT_WRITABLE, BUILT_IN_PRINCIPAL, OWN_ACCOUNT and OBJECT_NOT_IN_CREDENTIAL_SCOPE are decided by the Gateway before anything is sent.
404	NO_GROUP, NOT_A_GROUP, or NO_PRINCIPAL -- no principal {pid}. Nothing was written.
409	CYCLIC_MEMBERSHIP -- the key server refused because this edge would close a loop in group membership. Nothing was written. It is almost always the reverse membership: the group is already reachable as a member of the principal you are adding. This route does not walk the membership graph and cannot tell you which edge closed the loop. NOT_SAVED -- the key server did not refuse and the membership read-back does not contain the principal.
500	A fault rather than a refusal. OP_FAILED is the catch-all: the key server refused in words that match no classified pattern, so the Gateway cannot say more than that the operation did not happen. Some key server refusals that are conceptually a caller error arrive here rather than as a 4xx, because the wire carries no distinguishing code -- where a route can recognise one from its message it maps it, and each such mapping is documented on the operation.
503	A capacity ceiling or a missing deployment prerequisite. retryable says which. A scope of session or process names the ceiling that was hit, and the response carries Retry-After.