* sts: enforce session-policy explicit deny during role chaining
A chained AssumeRole caller authenticates with an STS session token whose
inline session policy can explicitly deny sts:AssumeRole. The deny check only
evaluated the caller's named policies, so such a session could still chain into
any role its trust policy admits. Validate the session token in the deny check
and honor an explicit Deny in the inline session policy too.
* test(sts): integration coverage for AssumeRole authorization
Add an end-to-end AssumeRole authorization test (real weed mini + boto3):
a non-admin caller assumes a role its trust policy admits, an explicit
identity-side deny is blocked, and a session policy's explicit deny blocks
role chaining.
* sts: skip OIDC tokens and reject revoked sessions in the chaining deny check
Review follow-ups on the session-policy deny check:
- Guard session validation with !isOIDCToken so a bearer token our STS service
cannot validate does not error into a false deny.
- Reject a revoked session before evaluating its policy, restoring the
revocation enforcement the AssumeRole path lost when it stopped routing
through IsActionAllowed.
* fix(sts): authorize AssumeRole by the role's trust policy
The role's trust policy already declares who may assume it, but the caller
also had to pass an identity-side sts:AssumeRole check that only the Admin
action could satisfy — legacy static identities have no way to express
sts:AssumeRole on a role. So assuming any role required a full admin
identity. Drop the redundant check and let the trust policy be the authority;
scope it to specific principals to restrict who can assume.
* sts: resolve caller principal ARN for the trust-policy check
A legacy static identity can reach AssumeRole without a PrincipalArn set;
passing the empty value would miss a trust policy that names a concrete
principal. Resolve it to the canonical user ARN, sharing the logic
GetCallerIdentity already used inline.
* sts: enforce explicit identity-side deny for AssumeRole
Authorizing a named role by its trust policy alone dropped identity-side
evaluation entirely, so a caller whose attached policy explicitly denies
sts:AssumeRole could still assume any role the trust policy admits. Re-check
the caller's policies through the IAM manager for an explicit deny
(deny-always-wins) without requiring an allow; the trust policy stays the
allow authority.
Chris Lu