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AWS CloudTrail
User Guide (Version 1.0)

Creating an Access Policy to Grant Access to a Third Party

Account A must create a separate IAM role for Account Z, the third-party analyzer in Scenario 2. When you create the role, AWS automatically creates the trust relationship, which specifies that Account Z will be trusted to assume the role. The access policy for the role specifies what actions Account Z can take. For more information about creating roles and role policies, see Creating a Role.

For example, the trust relationship created by AWS specifies that Account Z is trusted to assume the role created by Account A. The following is an example trust policy:

{ "Version": "2012-10-17", "Statement": [{ "Sid": "", "Effect": "Allow", "Principal": {"AWS": "arn:aws:iam::account-Z-id:root"}, "Action": "sts:AssumeRole" }] }

If you specified an external ID when you created the role for Account Z, your access policy contains an added Condition element that tests the unique ID assigned by Account Z. The test is performed when the role is assumed. The following example access policy has a Condition element.

For more information, see How to Use an External ID When Granting Access to Your AWS Resources to a Third Party in the IAM User Guide.

{ "Version": "2012-10-17", "Statement": [{ "Sid": "", "Effect": "Allow", "Principal": {"AWS": "arn:aws:iam::account-Z-id:root"}, "Action": "sts:AssumeRole", "Condition": {"StringEquals": {"sts:ExternalId": "external-ID-issued-by-account-Z"}} }] }

You must also create an access policy for the Account A role to specify that Account Z can read all logs from the Amazon S3 bucket. The access policy should look something like the following example. The wild card (*) at the end of the Resource value indicates that Account Z can access any log file in the S3 bucket to which it has been granted access.

{ "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": [ "s3:Get*", "s3:List*" ], "Resource": "arn:aws:s3:::bucket-name/*" }, { "Effect": "Allow", "Action": [ "s3:Get*", "s3:List*" ], "Resource": "arn:aws:s3:::bucket-name" } ] }

After you have created a role for Account Z and specified the appropriate trust relationship and access policy, an IAM user in Account Z must programmatically assume the role to be able to read log files from the bucket. For more information, see Assuming a Role.