This post implements Authorization Code Grant (3-legged OAuth) on Amazon ECS with secure session binding and scoped tokens. This post provides a working implementation with:

This solution uses OAuth 2.0 (RFC 6749) and OpenID Connect (OIDC). OIDC authenticates users (who they are), and OAuth 2.0 authorizes their actions (what they can do).

We focus on the Authorization Code Grant for user-delegated access. The user authenticates with an identity provider and grants consent. The application then exchanges an authorization code for an access token, which creates an audit trail.In this flow, the user authenticates with an identity provider and grants consent for the agent to access specific resources on their behalf. The application exchanges the resulting authorization code for a scoped access token which Amazon Bedrock AgentCore Identity secures in its token vault. Because each token is bound to a specific user identity with explicit consent, the solution maintains an auditable chain from user authentication through to agent action.

The Authorization Code Grant is suited for agentic workloads that act on behalf of users because it provides user consent before the agent can act, session binding that verifies the user who initiated the authorization request is the same user who granted consent, and scoped delegation that limits the agent to only the permissions the user approved.