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feat(join-auth): add key-ID rotation to signed join authorisations

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Prerequisite for wiring the allocator to publish rosters. The signing
key is a shared HMAC secret mounted into both the allocator and the
allocated game server; without a key ID, rotating it would invalidate
every authorisation already issued for an in-flight match, because a
server holding only the new key cannot verify a token signed with the
old one.

Add KeyID to JoinAuthorisation and append it to the canonical claim
bytes, so it is covered by the signature and cannot be repointed at a
different key than the one that actually signed. Allocated servers now
hold a set of currently-valid keys and select by ID: a rotation
publishes the new key alongside the old, and the old is dropped once no
live match can still reference it.

The key file becomes a JSON map of key ID to base64 key. A file of raw
key bytes is still accepted as a single key under the empty ID, which is
what an unrotated deployment and the kind fixture use.

Game/scripts/match_net.gd builds the canonical bytes independently, so
it changes in lockstep; the cross-language golden token in
test_match_net.gd is regenerated from the Go implementation and now
carries a key ID. Added tests cover accepting either key mid-rotation,
rejecting a retired key ID, and rejecting a token whose key ID was
swapped to name a key the server does hold.

Go suite and 223 Godot tests pass.
This commit is contained in:
Josh Creek
2026-09-05 10:36:06 +01:00
parent 5453e19761
commit b8bcc1f3c1
6 changed files with 135 additions and 18 deletions
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Game/tests/cases/test_match_net.gd
+52 -3
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@@ -168,13 +168,62 @@ func test_allocated_join_authorisation_verifies_canonical_hmac() -> void:
# This envelope is generated from server/domain.JoinAuthorisationBytes with
# HMAC-SHA256(test-key), proving the Godot verifier agrees with the Go
# canonical representation rather than merely checking token membership.
var token := "eyJBdXRob3Jpc2F0aW9uIjp7Ik1hdGNoSUQiOiJtYXRjaC0xIiwiU2VydmVySUQiOiJzZXJ2ZXItMSIsIlBsYXllcklEIjoicGxheWVyLTEiLCJTdGVhbUlEIjoic3RlYW0tMSIsIlNsb3QiOjUsIlRlYW0iOjEsIlByb3RvY29sIjoiMSIsIkdlbmVyYXRpb24iOjEsIkV4cGlyZXNBdCI6IjIwOTktMDgtMzFUMTI6MDA6MDBaIn0sIlNpZ25hdHVyZSI6Ijk0QkFOWjJpMkJUWHNWOVdaSWQ1dnE1Q3FqUXF4eGFXNnB4c2U0SFRXSDg9In0="
# Regenerate it whenever JoinAuthorisationBytes changes; a stale token here
# is exactly how a silent cross-language format drift would be caught.
var token := "eyJBdXRob3Jpc2F0aW9uIjp7Ik1hdGNoSUQiOiJtYXRjaC0xIiwiU2VydmVySUQiOiJzZXJ2ZXItMSIsIlBsYXllcklEIjoicGxheWVyLTEiLCJTdGVhbUlEIjoic3RlYW0tMSIsIlNsb3QiOjUsIlRlYW0iOjEsIlByb3RvY29sIjoiMSIsIkdlbmVyYXRpb24iOjEsIkV4cGlyZXNBdCI6IjIwOTktMDgtMzFUMTI6MDA6MDBaIiwiS2V5SUQiOiJrZXktMjAyNi0wOSJ9LCJTaWduYXR1cmUiOiJ4bWw1a09qdjltVURab256bHVFcitCM2wyQ0c4THBOUisxd0tpV1VkMjFrPSJ9"
var match_net := MatchNet.new()
assert_true(match_net.configure_join_authorisations([token], {"match_id": "match-1", "server_id": "server-1", "protocol": "1", "protocol_version": 1}, "test-key".to_utf8_buffer()), "HMAC roster configures")
assert_true(match_net.configure_join_authorisations([token], {"match_id": "match-1", "server_id": "server-1", "protocol": "1", "protocol_version": 1}, {"key-2026-09": "test-key".to_utf8_buffer()}), "HMAC roster configures")
assert_true(match_net._valid_join_authorisation(token), "Go-compatible canonical HMAC is accepted")
var tampered_payload: Dictionary = JSON.parse_string(Marshalls.base64_to_raw(token).get_string_from_utf8())
tampered_payload["Signature"] = "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA="
var tampered_token := Marshalls.raw_to_base64(JSON.stringify(tampered_payload).to_utf8_buffer())
var tampered_match_net := MatchNet.new()
assert_true(tampered_match_net.configure_join_authorisations([tampered_token], {"match_id": "match-1", "server_id": "server-1", "protocol": "1", "protocol_version": 1}, "test-key".to_utf8_buffer()), "tampered roster fixture configures")
assert_true(tampered_match_net.configure_join_authorisations([tampered_token], {"match_id": "match-1", "server_id": "server-1", "protocol": "1", "protocol_version": 1}, {"key-2026-09": "test-key".to_utf8_buffer()}), "tampered roster fixture configures")
assert_true(not tampered_match_net._valid_join_authorisation(tampered_token), "allowlisted but forged signature is rejected")
# Rotation contract: the allocator signs with one key while allocated servers
# accept the set of currently-valid keys, so rotating does not invalidate
# authorisations already issued for in-flight matches. All three envelopes are
# generated from server/domain.JoinAuthorisationBytes.
const ROTATION_CONTEXT := {"match_id": "match-1", "server_id": "server-1", "protocol": "1", "protocol_version": 1}
const TOKEN_SIGNED_WITH_OLD_KEY := "eyJBdXRob3Jpc2F0aW9uIjp7Ik1hdGNoSUQiOiJtYXRjaC0xIiwiU2VydmVySUQiOiJzZXJ2ZXItMSIsIlBsYXllcklEIjoicGxheWVyLTEiLCJTdGVhbUlEIjoic3RlYW0tMSIsIlNsb3QiOjUsIlRlYW0iOjEsIlByb3RvY29sIjoiMSIsIkdlbmVyYXRpb24iOjEsIkV4cGlyZXNBdCI6IjIwOTktMDgtMzFUMTI6MDA6MDBaIiwiS2V5SUQiOiJrZXktMjAyNi0wOCJ9LCJTaWduYXR1cmUiOiI5TW42eldERGNwR1pmblY2NXdreXNCYTduUnk3OG1QQkZPT29JN2F1UkdJPSJ9"
const TOKEN_SIGNED_WITH_NEW_KEY := "eyJBdXRob3Jpc2F0aW9uIjp7Ik1hdGNoSUQiOiJtYXRjaC0xIiwiU2VydmVySUQiOiJzZXJ2ZXItMSIsIlBsYXllcklEIjoicGxheWVyLTEiLCJTdGVhbUlEIjoic3RlYW0tMSIsIlNsb3QiOjUsIlRlYW0iOjEsIlByb3RvY29sIjoiMSIsIkdlbmVyYXRpb24iOjEsIkV4cGlyZXNBdCI6IjIwOTktMDgtMzFUMTI6MDA6MDBaIiwiS2V5SUQiOiJrZXktMjAyNi0wOSJ9LCJTaWduYXR1cmUiOiJ4bWw1a09qdjltVURab256bHVFcitCM2wyQ0c4THBOUisxd0tpV1VkMjFrPSJ9"
const TOKEN_SIGNED_WITH_RETIRED_KEY := "eyJBdXRob3Jpc2F0aW9uIjp7Ik1hdGNoSUQiOiJtYXRjaC0xIiwiU2VydmVySUQiOiJzZXJ2ZXItMSIsIlBsYXllcklEIjoicGxheWVyLTEiLCJTdGVhbUlEIjoic3RlYW0tMSIsIlNsb3QiOjUsIlRlYW0iOjEsIlByb3RvY29sIjoiMSIsIkdlbmVyYXRpb24iOjEsIkV4cGlyZXNBdCI6IjIwOTktMDgtMzFUMTI6MDA6MDBaIiwiS2V5SUQiOiJrZXktMjAyNy0wMSJ9LCJTaWduYXR1cmUiOiJRemFYLzB5T0pObE1oRXRPZ1BBcUpRNGJueHZRb1BVU09CR0p2Mm9nQVdnPSJ9"
func test_join_authorisation_accepts_every_key_in_the_rotation_set() -> void:
# Mid-rotation: both keys are published, so authorisations issued before
# and after the switch must both still admit their player.
var keys := {
"key-2026-08": "old-key".to_utf8_buffer(),
"key-2026-09": "test-key".to_utf8_buffer(),
}
for token in [TOKEN_SIGNED_WITH_OLD_KEY, TOKEN_SIGNED_WITH_NEW_KEY]:
var match_net := MatchNet.new()
assert_true(match_net.configure_join_authorisations([token], ROTATION_CONTEXT, keys), "rotation fixture configures")
assert_true(match_net._valid_join_authorisation(token), "a token signed by any currently-valid key is accepted")
func test_join_authorisation_rejects_a_key_id_outside_the_set() -> void:
# Rotation completed: the retired key is dropped, so anything still signed
# with it must stop being admitted.
var keys := {"key-2026-09": "test-key".to_utf8_buffer()}
var match_net := MatchNet.new()
assert_true(match_net.configure_join_authorisations([TOKEN_SIGNED_WITH_RETIRED_KEY], ROTATION_CONTEXT, keys), "retired-key fixture configures")
assert_true(not match_net._valid_join_authorisation(TOKEN_SIGNED_WITH_RETIRED_KEY), "a token naming a key outside the set is rejected")
func test_join_authorisation_key_id_cannot_be_repointed_at_another_key() -> void:
# KeyID is inside the signed bytes, so swapping it to name a key the server
# does hold must fail verification rather than selecting that key.
var payload: Dictionary = JSON.parse_string(Marshalls.base64_to_raw(TOKEN_SIGNED_WITH_OLD_KEY).get_string_from_utf8())
payload["Authorisation"]["KeyID"] = "key-2026-09"
var repointed := Marshalls.raw_to_base64(JSON.stringify(payload).to_utf8_buffer())
var keys := {
"key-2026-08": "old-key".to_utf8_buffer(),
"key-2026-09": "test-key".to_utf8_buffer(),
}
var match_net := MatchNet.new()
assert_true(match_net.configure_join_authorisations([repointed], ROTATION_CONTEXT, keys), "repointed fixture configures")
assert_true(not match_net._valid_join_authorisation(repointed), "the key ID is covered by the signature")