How can I see more information about which roles or permissions are attached to this assumed role?
You can access this information a number of ways, if you know the name of the role you can use the IAM service, here is a boto3 example:
import boto3
iam = boto3.resource('iam')
role = iam.Role('AWSServiceRoleForRDS')
for pol in role.attached_policies.iterator():
print(pol)
For me this gives:
iam.Policy(arn='arn:aws:iam::aws:policy/aws-service-role/AmazonRDSServiceRolePolicy')
The sole policy I have attached to this role. Obviously, you'll need to substitute the role name you are interested in here in place of 'AWSServiceRoleForRDS'
In general this will print out all the policies attached to the role (to stdout).
In order to do make this query you need to be authenticated as a user or role that has permissions to access the IAM role (or user).
Update: How to find the name of the role from an ARN?
following the aws docs for IAM identifies you can identify the role name from the arn for sts assumed roles they follow this format:
arn:aws:sts::account:assumed-role/role-name/role-session-name
Based on what was posted:
arn:aws:sts::123456789012:assumed-role/my-service-role/aws-sdk-1111111111111 is not authorized to perform: secretsmanager:GetSecretValue
it looks like my-service-role
is the name of the assumed role.