能否将AWS IAM作为Cognito提供商？实现指定AWS账号访问无服务器应用？

Great questions—let's break them down one by one to get you sorted for your serverless web app:

1. Can AWS IAM be used as an identity provider for AWS Cognito? #

Yes, though it’s commonly done via AWS IAM Identity Center (formerly AWS Single Sign-On) which builds on IAM’s core capabilities, using SAML 2.0 as the integration layer. Here’s how it works for typical use cases:

• Cognito User Pools: You can configure your user pool to accept a SAML 2.0 identity provider. Since IAM Identity Center supports SAML 2.0, you can set it up as the IdP, letting users authenticated through IAM Identity Center sign into your web app via Cognito. This is the standard flow for user-facing login experiences.
• Cognito Identity Pools (Federated Identities): If you just need to grant IAM users/roles access to backend AWS resources (rather than a full web app login flow), you can directly federate IAM identities with the identity pool. This skips the user pool but is useful for resource-specific access scenarios.

2. Does AWS Cognito support authentication and authorization only for specific AWS accounts? #

Absolutely—you have multiple ways to lock access down to users from specific AWS accounts:

• SAML IdP Restrictions (User Pools): When setting up your SAML IdP (like IAM Identity Center), you can add validation rules either in the Cognito user pool’s IdP settings or within the SAML assertion itself. For example, you can check that the assertion includes your target AWS account ID and reject any login attempts that don’t match.
• Identity Pool Trust Policies: For identity pools, modify the IAM role trust policies associated with the pool to restrict access to specific accounts. Add a condition like:

  "Condition": {
    "StringEquals": {
      "aws:PrincipalAccount": "123456789012"
    }
  }
  

  This ensures only identities from the specified account can assume the role and access your resources.
• Custom Lambda Triggers: For ultra-granular control, use Cognito’s pre-authentication or post-authentication Lambda triggers. In the trigger code, you can check the user’s associated AWS account ID and deny access if it’s not on your allowed list.

内容的提问来源于stack exchange，提问作者darthfather