Merge pull request 'ADR 0158: a provider with one credential shares it with every consumer, and the vault remakes it for all at once' (#246) from decision/0158-a-provider-with-one-credential-shares-it into main

2026-10-01 10:18:11 +00:00
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+---
+topic: the mesh
+status: accepted
+date: 2026-10-01
+deciders: jochen
+reconstructed: false
+extends: 02-DECISIONS/0048-a-provider-creates-the-credential-the-mesh-minted.md
+---
+
+# 158. A provider with one credential shares it with every consumer, and the vault remakes it for all of them at once
+
+## Context
+
+[ADR 0048](0048-a-provider-creates-the-credential-the-mesh-minted.md) gave every consumer of a
+provision its own credential: the mesh mints one per pair, the provider's own code creates the
+login, and rotating one consumer's touches nothing else. That is right for a database, a broker, an
+object store — software that can hold many logins.
+
+The media software on the home server cannot. A download client has one web password; an indexer
+has one API key; each of the library managers has one key in its configuration; the media server
+holds one token issued elsewhere. There is no login per consumer to create, so
+[ADR 0113](0113-the-vault-makes-every-secret.md)'s only remaining form applied: the value is
+*accepted*. On 2026-10-01 the home server held forty-seven accepted own secrets and twelve accepted
+pair credentials, every one rotatable only by a person changing the software by hand and accepting
+the new value, and one pair credential sat *made* and wrong because nobody could accept the real one.
+The operator asked for every password in the vault and rotatable, and for a library manager's
+definition to receive the download client's credential and address through provisioning like
+anything else (filed as the forge's issue 243 on this repository).
+
+The address half already works: the library manager requires the download client's API provision,
+the provider serves scheme, port and user name, and the binding carries them. Only the credential
+half had no form.
+
+## Considered Options
+
+1. **Keep accepting.** Honest about what the software can do and what the mesh cannot, and it is
+   the state the home server was in: nothing rotates, a consumer added later needs a person, and an
+   unknown predecessor password stays unknown for ever.
+2. **Put a login per consumer in front of the software.** A proxy that holds the one credential and
+   issues many. A second service per provider, with its own credential to keep, to make the mesh's
+   model fit software that does not share it.
+3. **Let the provider say its one credential is the credential.** An offer names which of the
+   provider's own secrets *is* what every consumer receives. The vault keeps one record, sealed to
+   the provider's machine, every current consumer's machine and the operator, and because it stores
+   no plaintext it cannot seal an existing value to a later consumer — so it **remakes the value
+   for all of them at once** whenever the set of consumers changes or a rotation is asked. The
+   provider takes it the way an own secret is taken ([ADR 0114](0114-a-shared-credential-rotates-over-two-credentials.md),
+   issue 180); consumers read it at start.
+
+## Decision
+
+**Option 3.** A provider whose software holds one credential shares that credential, and the mesh
+owns its whole lifecycle.
+
+- **The offer says so.** `{"name": "download-client-api", "credential": {"own": "password"}}` on a
+  provider's `provides` entry names one of its own secrets as the credential of that provision. The
+  named own secret must say how it is taken (`taken: at-start` or `taken: applied`); an offer
+  naming an undeclared or untaken secret is refused at parse.
+- **One record, many seals.** The vault keeps one value per (provider assignment, provision). It is
+  sealed to the provider's machine, to each consumer's machine that currently binds the provision,
+  and to the operator. Every consumer's binding file carries the provider's one user name and the
+  secret file carries the shared value; the shape a consumer reads is the pair credential's, so a
+  consumer's definition does not know whether its credential is shared.
+- **Remade for all, together.** When a consumer binds or unbinds, or `secret rotate` is asked on the
+  provider's own secret, the vault makes a new value and seals it to every current holder in one
+  act, and the mesh sends every holding machine. The provider restarts on the new value or applies
+  it at start; each consumer restarts on it. There is no window between two credentials, because
+  there is one credential; there is the restart, stated as the cost below.
+- **An accepted shared value is sealed to everyone the moment it is accepted.** `secret accept` on
+  the provider's own secret is the one moment the mesh holds the plaintext, and it seals copies for
+  every current consumer then. It is not remade afterwards ([ADR 0113](0113-the-vault-makes-every-secret.md)):
+  a consumer that binds later is refused until the value is accepted again, in words that say so.
+- **A value the software issues itself stays accepted.** A token the media server obtains from its
+  vendor cannot be set by the mesh; its provision keeps the accepted form until a module can deliver a
+  value it did not mint to the vault, which this record does not build.
+- **Nothing changes for software that holds many logins.** ADR 0048's form stays the default; this
+  is the form for an offer that says it has one credential.
+
+## Consequences
+
+- The media stack's six providers stop needing a person per consumer. A library manager binding
+  the download client gets a working credential the mesh made, and an unknown predecessor password
+  is replaced by one the mesh knows, recoverable with the operator's key.
+- **Adding or removing a consumer restarts every consumer of that provision and the provider.**
+  That is the price of one credential, and it is paid when a definition binds, not at an hour of
+  nobody's choosing. It is stated in the plan's words when it happens.
+- Rotation of a shared credential is [ADR 0114](0114-a-shared-credential-rotates-over-two-credentials.md)'s
+  single-party form across several machines: in place, all holders sent together. The staged form
+  for a backend that takes its credential once is still not built, and a provider whose own secret
+  says `applied` refuses rotation by name until it is.
+- The vault can name who holds a shared value — the copies are the record — so *who has this* stays
+  a query, as design 13 requires.
+- The accepted count on the home server becomes a list that shrinks, provider by provider, as each
+  one's start applies the file.
+
+## How this is checked
+
+| Rule | Checked by |
+|---|---|
+| An offer may name one of its own secrets as its credential; an undeclared or untaken secret is refused at parse | manifest tests |
+| A consumer of a shared provision receives the provider's value as its pair credential, under the provider's one user name | resolver and declaration tests |
+| The record is sealed to the provider, every current consumer and the operator; a consumer binding or unbinding remakes it for all | inventory tests against a raised store |
+| Rotating the provider's own secret remakes every holder's copy, and an accepted value is sealed to current consumers once and not remade | inventory tests |
+| Live: a library manager on the home server binds the download client with a value the mesh made, the client takes it at start, and a rotation through the console reaches both | done by hand after the media catalogue's providers apply the file at start |
+
+## References
+
+- [ADR 0048](0048-a-provider-creates-the-credential-the-mesh-minted.md) — extended: the per-consumer form stays the default; this is the form for one credential
+- [ADR 0113](0113-the-vault-makes-every-secret.md), [ADR 0114](0114-a-shared-credential-rotates-over-two-credentials.md) — the accepted form and the single-party rotation this rests on
+- [Issue 180](../04-ISSUES/180-a-modules-own-secret-cannot-be-rotated/00-report.md) — the `taken` word and the rotation this reuses
+- [Design 24 — The secrets vault](../03-DESIGN/01-to-be/24-the-secrets-vault.md), [Design 13 — Credentials and their rotation](../03-DESIGN/01-to-be/13-credentials-and-their-rotation.md)
+- The forge's issue 243 on this repository, where the operator's ask and the home server's count were recorded
@@ -171,6 +171,7 @@ python3 00-META/checks/index.py            fail if stale
 - **0154** — [The mesh's own verbs are the mesh-controller seat's tools, and which verbs those are](0154-the-meshs-own-verbs-are-the-controller-seats-tools.md)
 - **0156** — [An artifact is what a build produces, the artifact store serves every kind, and its seat is named for its scope](0156-an-artifact-is-what-a-build-produces-and-the-store-is-named-for-its-scope.md)
 - **0157** — [A build says what it does on the bus, as it happens](0157-a-build-says-what-it-does-on-the-bus-as-it-happens.md)
+- **0158** — [A provider with one credential shares it with every consumer, and the vault remakes it for all of them at once](0158-a-provider-with-one-credential-shares-it-with-every-consumer.md)

 ### Its tiers, from the bottom up

@@ -145,5 +145,7 @@ and the operator, and sends the machine, so the module starts again on it. A sec
 is refused with the word to write, because a credential rotated under software that never reads it
 again is the fault of issue 179 made deliberately; an applied one is refused until the staged form is
 built; an accepted one is refused as ADR 0113 says. `rotate` is a verb on the controller's seat with
-both shapes, so the console asks for either. *How it is checked:* the tests named in issue 180, and a
+both shapes, so the console asks for either. A provider that shares its one credential with every
+consumer ([ADR 0158](../../02-DECISIONS/0158-a-provider-with-one-credential-shares-it-with-every-consumer.md))
+rotates the same way, with every holder's copy remade and every holding machine sent together. *How it is checked:* the tests named in issue 180, and a
 live rotation through the console of a secret a module reads at start.
@@ -2,8 +2,9 @@
 layer: to-be
 status: implemented
 code: [mesh-catalog, mesh-controller, mesh-host]
-updated: 2026-09-21
+updated: 2026-10-01
 decisions:
+  - 02-DECISIONS/0158-a-provider-with-one-credential-shares-it-with-every-consumer.md
  - 02-DECISIONS/0094-a-module-may-hold-several-secrets-from-one-provider.md
  - 02-DECISIONS/0092-an-operator-delivers-a-pair-credential.md
  - 02-DECISIONS/0085-a-secret-is-a-provision.md
@@ -127,6 +128,22 @@ credential a provider grants; the export names each entry by the node and module
 the name they know it by, and says whether it is a module's own secret or a pair credential, so
 recovery addresses both alike.

+### A provider with one credential
+
+*Decided 2026-10-01 ([ADR 0158](../../02-DECISIONS/0158-a-provider-with-one-credential-shares-it-with-every-consumer.md)); to be built.*
+
+Software that holds one credential — a download client's web password, an indexer's one API key —
+cannot give each consumer a login, so ADR 0048's form does not fit it and its values were accepted
+by hand. An offer may now say `"credential": {"own": "<secret>"}`: the provider's own secret *is* the
+credential every consumer of that provision receives, in the shape of an ordinary pair credential,
+under the provider's one user name. The vault keeps one value per provider assignment and provision,
+sealed to the provider's machine, each consumer's machine and the operator; because it holds no
+plaintext it remakes the value for every holder at once when a consumer binds or unbinds or a
+rotation is asked, and the mesh sends every holding machine together. The provider takes it as it
+says it takes its own secret (`taken`, issue 180); consumers read it at start. An accepted value is
+sealed to the consumers of the moment and not remade; a consumer that binds later waits for the next
+acceptance. *How it is checked:* the rows of ADR 0158's table, once built.
+
 ## Beyond generate and hold

 Owning a secret means owning more than its creation. The mesh being migrated onto has a working