AXIAM PHP SDK

Keys are sourced via OIDC discovery (GET /.well-known/openid-configuration -> jwks_uri, falling back to {baseUrl}/oauth2/jwks if discovery is unavailable or omits jwks_uri), TTL-cached, and refetched exactly once when an unknown kid is encountered before failing closed.

Two security invariants (every sibling SDK independently confirmed both):

• Pitfall 5 / T-alg-confusion: the header alg is pinned to EdDSA BEFORE any key lookup is attempted. A token never gets to choose its own verification algorithm.
• Pitfall 3 / T-cross-tenant: GET /oauth2/jwks is organization-wide, not tenant-scoped, so a validly-signed token for a different tenant under the same organization must still be rejected. The tenant_id claim is checked AFTER signature verification succeeds.

Deliberately does NOT use firebase/php-jwt's CachedKeySet convenience class — it requires a PSR-18 client + PSR-17 request factory + PSR-6 cache pool, a dependency chain D-07 explicitly avoids. This hand-rolled TTL cache mirrors every sibling SDK's own JWKS-cache shape (e.g. the Python SDK's _jwks.py).

verify() never throws on attacker-controlled token input — malformed/short/ non-3-part tokens, unknown algorithms, unknown kids, and bad signatures all return null (fail closed). The only thrown exception is the ext-sodium-missing guard, which is an environment/deployment misconfiguration, not attacker input.