Tutorial / Cram Notes
AWS Security Token Service (STS) is an invaluable component of the AWS ecosystem, particularly when it comes to managing temporary credentials for accessing AWS services. Understanding when to leverage AWS STS can be crucial for enhancing security and ensuring that the principle of least privilege is maintained across your AWS environments. This concept is especially pertinent for individuals preparing for the AWS Certified Security – Specialty (SCS-C02) exam, which emphasizes security best practices within AWS.
What is AWS STS?
AWS STS is a service that enables you to request temporary, limited-privilege credentials for AWS Identity and Access Management (IAM) users or for users that you authenticate (federated users). These credentials are designed to expire automatically, reducing the risk of compromised long-term credentials.
Scenarios for Using AWS STS
Federated User Access
When integrating third-party users or services into your AWS environment, leveraging federation with AWS STS allows you to avoid creating permanent IAM users. Instead, you provide them with temporary access using the identity provider of your choice, such as SAML 2.0 or OpenID Connect.
For example, an organization using corporate credentials to access AWS can use AWS STS to grant employees temporary access to AWS resources based on their corporate permissions, without needing an IAM account for each employee.
Cross-Account Access
In scenarios where you need to allow users or services from one AWS account to access resources in another, AWS STS can help facilitate this by providing temporary credentials that can assume a role in the target account with the necessary permissions.
Example:
- Account A has a user who needs to access a resource in Account B.
- Account B provides a role with specific permissions necessary for the task.
- Account A’s user assumes the role in Account B using AWS STS to obtain temporary credentials.
Temporary Elevated Access
When a user or service requires elevated permissions for a short duration to perform a specific task, AWS STS can be used to grant temporary security credentials that provide the necessary increased privileges.
Imagine a scenario where a developer needs to deploy a new version of a service. You can use AWS STS to grant necessary permissions during the deployment window.
Mobile Applications and Temporary Sessions
Mobile applications can utilize AWS STS to provide end-users with temporary credentials that have limited permissions, enough to interact securely with AWS services without embedding long-term AWS credentials in the application.
Comparing Permanent IAM Users to Temporary STS Credentials
| Attribute | Permanent IAM User Credentials | Temporary STS Credentials |
|---|---|---|
| Expiration | Never expire naturally | Automatically expire |
| User Management Overhead | Higher (need to manage users and their keys) | Lower (credentials are temporary and users are often federated) |
| Risk of Compromise | Higher risk if keys are leaked | Lower as credentials are temporary |
| Flexibility | Less flexible; permissions attached directly to the user | More flexible; permissions can vary with each credential issuance |
| Cross-Account Access | Requires explicit trust policies and roles | Ideal for cross-account scenarios using role assumptions |
Best Practices for Using AWS STS
- Set the expiration period of the AWS STS temporary credentials to the shortest duration that your use case permits. This minimizes potential exposure if credentials are compromised.
- Use AWS STS to implement role assumption policies, using different roles that have tightly scoped permissions for specific tasks.
- Apply conditions to the STS token to further restrict usage, such as time of day or client IP address constraints.
- Monitor usage of STS tokens using AWS CloudTrail, which logs all STS API calls, allowing for security audits and analyses.
- Avoid embedding long-term AWS credentials in applications; instead, use STS to provide the necessary temporary access with limited permissions.
Conclusion
Using AWS STS to issue temporary credentials aligns with best practices for securing AWS environments. By understanding the scenarios where AWS STS is the optimal solution, you can ensure that your AWS architecture follows the principle of least privilege, reduces management overhead, and mitigates the risk of long-term credential exposure. Applying this knowledge, as outlined for the AWS Certified Security – Specialty (SCS-C02) exam, enables you to architect and maintain a secure AWS infrastructure.
Practice Test with Explanation
AWS Security Token Service (STS) is used to grant users temporary access to AWS resources.
- True
- False
Answer: True
Explanation: AWS STS allows you to issue temporary, limited-privilege credentials to users so they can access AWS resources.
Temporary credentials issued by AWS STS can be configured to last for several years.
- True
- False
Answer: False
Explanation: Temporary credentials issued by AWS STS can last for a few minutes to several hours, but they cannot be set to last for years.
Which AWS service allows federation with an external identity provider?
- AWS IAM (Identity and Access Management)
- AWS KMS (Key Management Service)
- AWS Organizations
- AWS STS (Security Token Service)
Answer: AWS STS (Security Token Service)
Explanation: AWS STS enables you to request temporary, limited-privilege credentials for AWS resources, which supports identity federation by allowing external identity systems to grant access to AWS resources.
You can use AWS STS to assume an IAM role within the same AWS account or another AWS account.
- True
- False
Answer: True
Explanation: AWS STS allows you to assume an IAM role within your own account or cross-account access.
Which of the following scenarios is most appropriate for using AWS STS?
- To assign long-term access policies to IAM users
- To enable access for an application that runs on an EC2 instance which requires AWS credentials
- To grant temporary security credentials to mobile app users accessing AWS services
- To create new permanent IAM roles
Answer: To grant temporary security credentials to mobile app users accessing AWS services
Explanation: AWS STS is ideal for providing temporary credentials to users who need access to AWS resources, such as mobile app users.
Which AWS feature provides you with a token after authenticating with your corporate credentials?
- AWS IAM permissions
- AWS STS temporary security tokens
- AWS KMS key policies
- AWS Direct Connect
Answer: AWS STS temporary security tokens
Explanation: After authenticating with corporate credentials, AWS STS provides a token you can use for a specified duration to access AWS resources.
AWS STS generated credentials can be used with AWS Command Line Interface (CLI).
- True
- False
Answer: True
Explanation: Users can configure the AWS CLI with temporary security credentials obtained from AWS STS to make programmatic calls to AWS services.
AWS STS is not available in all AWS regions.
- True
- False
Answer: False
Explanation: AWS STS is a global service with endpoints in all AWS regions, but it can also be used to request tokens for the global endpoint.
Which command is used to retrieve temporary credentials using AWS STS?
- get-session-token
- assume-role
- get-role-credentials
- authenticate-user
Answer: assume-role
Explanation: The assume-role command is used in AWS STS to request temporary credentials for a role you have permission to assume.
For a web application running on an EC2 instance that needs to access S3, what is the recommended way to manage credentials?
- Hard code AWS credentials into the application
- Use an EC2 instance profile that provides temporary credentials from AWS STS
- Save AWS credentials in a text file on the instance
- Use long-term IAM user credentials stored in environment variables
Answer: Use an EC2 instance profile that provides temporary credentials from AWS STS
Explanation: An EC2 instance profile is the best practice to manage credentials, as it provides temporary security credentials automatically to an EC2 instance.
Interview Questions
What is AWS Security Token Service (AWS STS) and what are its primary use cases?
AWS Security Token Service (AWS STS) is a web service that enables you to request temporary, limited-privilege credentials for AWS Identity and Access Management (IAM) users or for users that you authenticate (federated users). Its primary use cases include granting access to AWS resources in a secure manner for applications running on EC2 instances, for users that require access to AWS resources on a temporary basis, and for identity federation with external systems.
Can you explain the concept of federation in the context of AWS STS?
Federation in the context of AWS STS refers to the process of allowing users who already have identities outside of AWS (like in a corporate directory) to access AWS resources without having to create an IAM user for each identity. AWS STS facilitates federation by enabling these external users to assume temporary IAM roles with policies that grant them access to the necessary AWS resources.
How does AWS STS differ from IAM roles and when should you prefer using STS over IAM roles directly?
AWS STS is used to request temporary security credentials which can be used to assume an IAM role. An IAM role is an AWS entity with permission policies that determine what the entity can and cannot do in AWS. You should use AWS STS over IAM roles directly when you need to provide access to AWS resources for users or services that don’t have permanent AWS credentials or for short-term access requirements, minimizing long-term security risks.
What are the benefits of using temporary credentials over long-term access keys?
Temporary credentials, such as those provided by AWS STS, offer several benefits:
– They reduce the risk of long-term credentials being compromised.
– They automatically expire after a short duration, which limits the time window for potential misuse.
– They can be tied to a specific session, IP, or a set of permissions, adding an extra layer of security.
– They help in adhering to the principle of least privilege, granting only the permissions necessary for a specific task.
In what scenarios is it appropriate to use AWS STS for cross-account access?
AWS STS is ideal for cross-account access scenarios where users or services in one AWS account need to perform actions in another AWS account. It is appropriate when you want to abide by the principle of least privilege, granting only the necessary permissions, and when you prefer not to share long-term security credentials between accounts.
When is it recommended to use temporary credentials through AWS STS for accessing AWS resources from mobile applications?
It is recommended to use temporary credentials through AWS STS for mobile applications to provide secure access to AWS resources. This approach avoids storing long-term AWS credentials on the mobile device, which could be compromised. Temporary credentials enable you to grant access that is narrowly scoped to the needs of the application and expire after a short duration.
Describe the process of obtaining temporary credentials for a federated user with AWS STS.
To obtain temporary credentials for a federated user with AWS STS:
– Use a SAML assertion or an OpenID Connect token from your identity provider to call AssumeRoleWithSAML or AssumeRoleWithWebIdentity on AWS STS.
– AWS STS returns temporary security credentials that the federated user can use to make requests to AWS resources.
– The federated user uses these credentials in their AWS API calls, and the credentials automatically expire after the specified duration.
What are the limitations of the temporary credentials issued by AWS STS?
Temporary credentials issued by AWS STS have the following limitations:
– They are valid for a configurable duration, from a few minutes up to a maximum of 36 hours (12 hours is the default).
– They cannot be used to perform actions that require MFA if the role does not include session policies enforcing MFA authentication.
– Certain AWS services do not support the use of temporary credentials; you need to check service-specific documentation.
How does AWS STS provide encrypted communication and ensure the security of temporary credentials?
AWS STS provides encrypted communication by using HTTPS to issue temporary credentials, ensuring that the credentials cannot be intercepted in transit. Furthermore, the temporary credentials themselves are automatically expired by AWS STS after a certain period, which reduces the risk associated with potential exposure or misuse of credentials.
Can you explain the role of IAM policies when issuing temporary credentials with AWS STS, and how do you ensure the least privilege principle is applied?
IAM policies define the permissions that are associated with the temporary credentials issued by AWS STS. When you create a role or assume a role via STS, you can specify the policy that outlines the specific actions and resources that are allowed. To ensure the least privilege principle is applied, you should craft the IAM policies to include only the necessary permissions, aligning with the specific tasks the temporary credentials are intended for.
How does AWS STS interact with other AWS services, like Amazon EC2, when issuing temporary credentials for applications running on EC2 instances?
AWS STS interacts with Amazon EC2 through the use of IAM roles for EC You can attach an IAM role with proper permission policies to an EC2 instance. Applications running on that instance can then use the AWS SDK or CLI to request temporary credentials from AWS STS. These credentials are automatically provided to the instance’s role with no need for explicit retrieval, enabling secure access to other AWS services without embedding long-term credentials in the application.
What are best practices for monitoring and auditing the use of temporary credentials issued by AWS STS?
Best practices for monitoring and auditing temporary credentials include:
– Enable AWS CloudTrail to log all STS API calls; review these logs regularly.
– Use AWS CloudWatch to monitor API call patterns and set alarms for suspicious activities.
– Employ AWS Config to monitor compliance of the use of STS credentials with your organizational policies.
– Apply tags to IAM roles used with STS to organize and identify usage for audit and billing purposes.
– Regularly audit IAM roles and policies to ensure the least privilege principle is being maintained.
Great blog post! The explanation of AWS STS and its use cases was very clear.
I appreciate the detailed example of issuing temporary credentials using STS. It made the concept much easier to grasp.
Can someone explain the advantage of using AWS STS over creating long-lived IAM roles?
So, would you use AWS STS in a situation where users need temporary access to resources without creating a permanent IAM policy?
Thanks for this information, it’s very helpful.
Interesting read. How would you use STS with EC2 instances?
Appreciate the clarity on STS and temporary credentials. This will definitely help in my SCS-C02 exam preparation.
One question: how long can the temporary credentials issued by AWS STS last?