git:20260210.2b17bc4 to git:20260224.b517efb

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name: aws-iam

description: AWS IAM deep-dive skill - principal types, policy evaluation, STS assume role, SCP guardrails, KMS key policies/grants, and AccessDenied debugging. Use when designing AWS authz/authn, cross-account access, or troubleshooting IAM/KMS/SCP AccessDenied errors.

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# AWS IAM

## When to use

Use this skill when you are working on:

- IAM principals (users, roles, assumed-role sessions, service principals)

- Trust policies (`sts:AssumeRole*`) and cross-account access

- Identity-based vs resource-based policies

- Permission boundaries, session policies, and Organizations SCPs

- KMS key policies, grants, and `kms:Decrypt` / `kms:GenerateDataKey` failures

- Debugging `AccessDenied` in AWS (including cross-account and KMS)

## What to do (workflow)

1. Identify the **runtime principal** (often an STS assumed-role ARN)

2. Identify the **action** + **resource ARN(s)** from the error or design requirement

3. Determine which **policy layers** are in play:

- identity-based policy

- resource-based policy

- permission boundary

- session policy

- SCP (Organizations)

4. Look for **explicit deny** first (it wins)

5. For cross-account flows:

- validate the trust policy (who can assume)

- validate the permission policy (what the role can do)

- validate any resource policy (who can access the target resource)

6. For KMS:

- validate key policy + IAM policy + any grant constraints

## References

- `references/iam-authorization-model.md`

- `references/cross-account-and-externalid.md`

- `references/kms-key-policy-and-grants.md`

- `references/eks-pod-identity-abac-and-lattice.md`