Bearer tokens are widely used security mechanisms that provide secure access to resources over the internet. They are often used for authentication and authorization in modern application’s communication. As an AWS Certified Developer, it’s important to know how these tokens, including JSON Web Tokens (JWT), OAuth, and AWS Security Token Service (AWS STS), work and can be implemented in AWS platforms.
JSON Web Tokens (JWT)
JWTs are an open standard (RFC 7519) that defines a compact and self-contained way of transmitting information between parties as a JSON object. This information can be verified and trusted because it is digitally signed. JWTs can be signed by a secret (with the HMAC algorithm) or a public/private key pair using RSA or ECDSA.
In AWS, JWT Tokens are used in a variety of ways, such as user sign-in flows, application-to-application authentication, and even for temporary security credential issuance.
An example use case within AWS is the use of JWT tokens for User Pool in Amazon Cognito.
Here is the format of a JWT token:
{
“alg”: “HS256”,
“typ”: “JWT”
}
{
“sub”: “1234567890”,
“name”: “John Doe”,
“iat”: 1516239022
}
HMACSHA256(
base64UrlEncode(header) + “.” +
base64UrlEncode(payload),
secret)
}
OAuth
OAuth is not a token but a delegation protocol widely used on the Web. With OAuth, a user can delegate access to a third-party application without sharing their credentials (username and password). The token used in this process, which is often a JWT, is what grants the third-party application access to the user’s data.
As an AWS developer, you might use OAuth mechanisms to grant third-party applications access to AWS services. AWS Cognito supports authentication with identity providers through SAML or OAuth.
AWS Security Token Service (AWS STS)
Amazon’s AWS STS service 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). This service is particularly useful for situations where you need to delegate access to your AWS environment or to create temporary security credentials.
AWS STS generates a set of temporary credentials (AccessKeyId, SecretAccessKey, and a security token) that you can use to access AWS services. These are similar in nature to the long-lived AWS Key ID and Secret Key, but are automatically expired after a short period of time.
Here’s a sample of AWS STS temporary credentials:
{
“AccessKeyId”: “ASIAIOSFODNN7EXAMPLE”,
“SecretAccessKey”: “wJalrXUtnFEMI/K7MDENG/bPxRfiCYzEXAMPLEKEY”,
“SessionToken”: “AQoDYXdzEPT//////////wEXAMPLEtc764bNrC9SAPBSM22wDOk4x4HIZ8j4FZTwdQWLWsKWHGBuFqwAeMicRXmxfpSPfIeoIYRqTflfKD8YUuwthAx7mSEU/skwpZR9T0RQQGDG6hQ==”,
}
In conclusion, bearer tokens such as JWT, OAuth, and AWS STS are critical components for securing access to online resources. For an AWS Certified Developer – Associate, understanding these tokens is essential to setting up secure, scalable, and robust applications on AWS.
Practice Test
True or False: JSON Web Token (JWT) is a way of representing claims securely between two parties.
- True
- False
Answer: True
Explanation: JWT is indeed a way of representing claims securely between two parties. It is often used for authentication and secure information exchange.
Which of the following are use cases for AWS Security Token Service (STS)?
- A) Web identity federation
- B) Server-side token validation
- C) Mobile app management
- D) None of the above
Answer: A) Web identity federation
Explanation: AWS STS is primarily used for granting limited-privilege access to AWS services. One such use case is web identity federation.
True or False: An OAuth3 access token is essentially a JWT.
- True
- False
Answer: False
Explanation: While both OAuth3 tokens and JWTs are used to secure data transmission, an OAuth3 token is not inherently a JWT. OAuth3 tokens can be of any type and are not required to be JWTs.
What is the primary purpose of a Bearer Token?
- A) User identification
- B) Authorize access
- C) Encrypt data
- D) Both A & B
Answer: D) Both A & B
Explanation: A Bearer Token serves as both identification and access authorizer. It allows the user to access the resources they are permitted to use.
Which among the following is NOT a part of a JWT?
- A) Header
- B) Signature
- C) Key
- D) Payload
Answer: C) Key
Explanation: A JWT consists of three parts: a header, a payload, and a signature. The key is not a separate part of the token; rather, it’s used in creating the signature.
True or False: AWS STS tokens cannot be used to make direct AWS service requests.
- True
- False
Answer: False
Explanation: You can indeed use AWS STS tokens to make direct requests to AWS services.
Which HTTP authorization scheme does a Bearer Token employ?
- A) Digest
- B) OAuth
- C) Bearer
- D) AWS4-HMAC-SHA256
Answer: C) Bearer
Explanation: Bearer Tokens employ the Bearer HTTP authorization scheme, hence the name.
OAuth3 Framework supports which of the following flows?
- A) Authorization Code Grant
- B) Refresh Token Grant
- C) Implicit Grant
- D) All of the above
Answer: D) All of the above
Explanation: The OAuth3 framework supports multiple authorization flows, including Authorization Code Grant, Implicit Grant, and Refresh Token Grant.
What purpose does the AWS STS AssumeRole API serve?
- A) It rotates the encryption key.
- B) It allows you to assume a role and return a set of temporary security credentials.
- C) It manages the user’s account settings.
- D) None of the above
Answer: B) It allows you to assume a role and return a set of temporary security credentials.
Explanation: The AWS STS AssumeRole API call lets you assume a role and get back a set of temporary security credentials to access resources in a secure way.
Does the JWT payload contain sensitive user information?
- A) Always
- B) Never
- C) Only when encrypted
- D) It depends on the specific implementation
Answer: D) It depends on the specific implementation
Explanation: The decision to include sensitive user data in the JWT payload depends on the specific implementation. It’s typically avoided, as JWT is not inherently encrypted. However, it is possible to include such information if the JWT is encrypted.
Interview Questions
What is a JSON Web Token (JWT) used for in OAuth?
JWT is used to securely transfer information between parties. In OAuth, it is often used as an access token to authorize requests. The token carries information about the client and the user, ensuring that the service only discloses confidential information to the correct, authenticated client.
What does AWS Security Token Service (AWS STS) provide for applications?
AWS STS is a web service that provides short-term, limited-privilege credentials for AWS Identity and Access Management (IAM) users. These temporary security credentials can be used by applications to request access to AWS resources.
How are bearer tokens used within OAuth?
In OAuth, a bearer token is used to authorize the client. This token proves the client’s identity and gives permissions to the client based on the scope of the token.
In context of AWS STS, what is a role?
A role in AWS STS is an IAM identity that can be created in your account that has specific permissions. It is similar to a user, but it is not associated with a specific person. Rather, it’s intended to be assumable by trusted entities, such as AWS services, applications, or even users from a different account.
How long can AWS STS credentials last?
AWS STS credentials can last anywhere between a few minutes to several hours, however, the typical maximum duration is 12 hours. The exact duration can be set by the person who requested the credentials.
Why is it recommended to use AWS STS in a multi-tenant application?
It is recommended to use AWS STS in a multi-tenant application because it provides temporary security credentials that the application can use to sign AWS requests. This adds an additional level of security as the temporary nature of the credentials reduces the risk associated with long-term credentials.
In an OAuth flow, what is the purpose of the Authorization Server?
An Authorization Server in an OAuth flow authenticates the resource owner’s identity and issues access tokens to the client after obtaining appropriate authorization.
What format are JWT tokens in?
JWT tokens are in JSON format. They consist of three parts separated by dots, which are Header, Payload and Signature.
What are the advantages of using JWT over other types of tokens?
JWT has several advantages such as being self-contained and stateless, meaning all the necessary information is stored within the token itself. This makes it scalable and decouples the server from the clients, allowing it to be used across multiple servers without the need for token storage.
How are AWS STS credentials returned after a successful AssumeRole API call?
The AWS STS AssumeRole API call returns a set of temporary security credentials comprised of an access key ID, a secret access key, and a session token.
How does OAuth protect user credentials?
OAuth protects user credentials by making API requests on behalf of the user without exposing the user’s password. Instead, the user’s credentials are traded for a bearer token, which is used to authenticate further requests.
How are JWT tokens validated?
JWT tokens are validated by checking the signature that was created with the secret key. The server would decode the JWT and recompile it without the signature to compare it with the incoming token. If both match, then the token is validated.
Can you extend the expiration time of an active AWS STS token?
No, you cannot extend the expiration time of an active AWS STS token. Once a token is issued, its expiration time is fixed and cannot be changed. However, you can request a new token as needed.
How would a system differentiate between different OAuth scopes?
OAuth scopes are used to grant different levels of access to different resources. Each scope corresponds to a different level of access, and as such, these are usually differentiated by their unique names within the system.
What are potential risks of using bearer tokens?
The main risk of using bearer tokens is that if they are intercepted or leaked, they can be used by anyone to impersonate the user and gain unauthorized access to resources. To mitigate this, it is important to ensure secure transmission and storage of tokens.
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