Evolution of a JWT (JSON Web Token) Within a Domain
A JWT is primarily a self-contained token.
It includes all the necessary information about the user or entity within the token itself, eliminating the need for external server-side storage during its validation process. This characteristic makes JWTs stateless and ideal for distributed systems, as every component involved in the authentication process can independently verify the token without querying a central database.
What “Self-Contained” Implies:
1. Encoded Information:
• The payload of the JWT contains claims (e.g., user ID, roles, or permissions), which describe the entity.
• Example:
{
"sub": "1234567890",
"name": "John Doe",
"role": "admin",
"iat": 1696843471
}
• These claims are signed to ensure they haven’t been tampered with.
2. Statelessness:
• The token itself carries all the data required for verification (e.g., user identity, issued timestamp, roles), so no session or state management is needed on the server side.
• Servers validate tokens by using the secret key or public key (in case of asymmetric encryption), instead of maintaining sessions.
3. Decentralised Verification:
• Any server or service that holds the signing key can verify and decode the token, enabling scalable architectures like microservices.
4. Drawback - Limited Revocation Mechanism:
• Since JWTs are self-contained and stateless, they cannot easily be revoked once issued unless additional mechanisms, like revocation lists or token expiration, are implemented.
In essence, a self-contained JWT streamlines authentication by embedding relevant claims directly in the token, making it portable, efficient, and independent of external storage systems.
However, when mutability is introduced within a specific domain, its contents (the “payload”) might be dynamically updated to reflect changes in the entity’s state or attributes. Consider the name claim in your JWT:
{
"sub": "1234567890",
"name": "Tarah Querfurt",
"iat": 1696843471
}
Over time, the name field may be updated to reflect changes in identity (e.g., a legal name change). Other claims, such as roles or permissions, might also evolve, e.g.,:
{
"sub": "1234567890",
"name": "Tarah Quinlan",
"iat": 1696843471,
"role": "owner"
}
Key Considerations for Mutable Tokens
1. Stateful Mutation Mechanisms:
• While JWTs are designed to be stateless, adding mutability implies using external mechanisms (e.g., token revocation lists or a central authority that can validate updated tokens).
• Example: A claims service can issue tokens dynamically based on the latest data from a database.
2. Auditing and Versioning:
• Version tracking of tokens becomes critical when claims change. For example, to ensure that audit logs remain consistent, older versions of tokens may need to be retained.
3. Security Risks:
• Mutability can introduce vulnerabilities. For example, if the token is updated without sufficient validation, unauthorised changes could escalate privileges.
Expanding Token Meanings Beyond a Domain
When a token is shared or used outside its originating domain, its claims may take on new meanings depending on external policies and expectations. Consider how the role claim in the example is interpreted:
Within Domain:
"role": "owner"
• The domain might associate owner with complete administrative rights.
Outside Domain:
• A partner system might interpret owner differently, such as limited rights to modify certain resources but not full control.
To ensure interoperability:
1. Namespace Claim Names:
• Use namespaces (e.g., example.com/role) to prevent ambiguous interpretation outside the domain.
2. Token Translation Layers:
• Introduce middleware to map claims into terms relevant to external systems.
Design Considerations
1. Compactness:
• For a mutable token, keeping claims lean avoids unnecessary bandwidth use. Avoid redundant claims by separating static identifiers (sub) from dynamic ones (role).
2. Stateless vs. Stateful:
• While JWTs are designed to avoid server-side state, introducing mutability requires systems like centralised token stores to manage the latest versions of tokens.
3. Extensibility:
• Claims should be flexible to accommodate changes. For example, a meta claim can be added to contain versioning or timestamp data for claim updates.
4. Encapsulation:
• JWTs can be wrapped in encrypted JWTs (JWE) for confidentiality and security in transit.
Object-Oriented Token Characteristics
In Object-Oriented Programming (OOP), a JWT token could be described as a mutable or immutable object depending on its design:
1. As an Immutable Object:
• Once issued, it remains unchanged. Updates require issuing a new token.
• Example in OOP terms:
const jwtToken = new ImmutableJWT({ sub: "1234567890", role: "admin" });
2. As a Mutable Object:
• The token’s properties can be updated via setters or external APIs:
jwtToken.setRole("owner");
Microservices Interaction with Tokens
Microservices can handle JWTs as a single source of truth for authorisation and identity:
• Token Validation: Services validate the token’s signature to confirm its integrity and source.
• Token Augmentation: A microservice might add or update claims (e.g., add permissions):
{
"sub": "1234567890",
"name": "Tarah Querfurt",
"permissions": ["read", "write", "execute"]
}
• Token Forwarding: The updated token can be forwarded to downstream services.
Summary
JWTs offer a lightweight, extensible mechanism for encoding identity. While typically immutable, their mutability can unlock dynamic role management within a domain.
However, their use across domains requires careful design to avoid misinterpretation. These considerations—compactness, statelessness, and security—ensure that tokens remain a robust component of modern microservice architectures.
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