Which AWS service is primarily used for implementing user identities across various AWS resources?

AWS Identity and Access Management (IAM) is the service designed primarily for managing user identities and permissions across various AWS resources. IAM allows you to create and manage AWS users and groups, and it provides them with specific permissions to access AWS resources.

By using IAM, you can enforce security policies by defining who can access what resources, under what conditions, and with what level of access. This capability is crucial for maintaining security and compliance within an AWS environment. IAM integrates with other AWS services seamlessly, allowing for fine-grained access control, role-based access, and multi-factor authentication, thereby enhancing the security and management of user identities across AWS.

While AWS Directory Service provides a way to manage directory-aware applications and services in the cloud, and AWS Cognito is focused on user sign-up, sign-in, and access control for mobile and web applications, IAM is the primary service for defining user access policies for a broader range of AWS services and resources. AWS Config is mainly used for monitoring and auditing resource configurations rather than managing identities.