JWT

Authorization Middleware for Caddy

This middleware implements an authorization layer for Caddy based on JSON Web Tokens (JWT). You can learn more about using JWT in your application at jwt.io.

Basic Syntax

jwt [path]

By default every resource under path will be secured using JWT validation. To specify a list of resources that need to be secured, use multiple declarations:

jwt [path1]
jwt [path2]

Important You must set the secret used to construct your token in an environment variable named JWT_SECRET. Otherwise, your tokens will always silently fail validation. Caddy will start without this value set, but it must be present at the time of the request for the signature to be validated.

Advanced Syntax

You can optionally use claim information to further control access to your routes. In a jwt block you can specify rules to allow or deny access based on the value of a claim.

jwt {
   path [path]
   allow [claim] [value]
   deny [claim] [value]
}

To authorize access based on a claim, use the allow syntax. To deny access, use the deny keyword. You can use multiple keywords to achieve complex access rules. If any allow access rule returns true, access will be allowed. If a deny rule is true, access will be denied. Deny rules will allow any other value for that claim.

For example, suppose you have a token with user: someone and role: member. If you have the following access block:

jwt {
   path /protected
   deny role member
   allow user someone
}

The middleware will deny everyone with role: member but will allow the specific user named someone. A different user with a role: admin or role: foo would be allowed because the deny rule will allow anyone that doesn't have role member.

Ways of passing a token for validation

There are three ways to pass the token for validation: (1) in the Authorization header, (2) as a cookie, and (3) as a URL query parameter. The middleware will look in those places in the order listed and return 401 if it can't find any token.

Method	Format
Authorization Header	Authorization: Bearer <token>
Cookie	"jwt_token": <token>
URL Query Parameter	/protected?token=<token>

Constructing a valid token

JWTs consist of three parts: header, claims, and signature. To properly construct a JWT, it's recommended that you use a JWT library appropriate for your language. At a minimum, this authorization middleware expects the following fields to be present:

Header

{
"typ": "JWT",
"alg": "HS256|HS384|HS512"
}

See progress on BTBurke#3 if you're interested in public key signing algorithms.

Claims

If you want to limit the validity of your tokens to a certain time period, use the "exp" field to declare the expiry time of your token. This time should be a Unix timestamp in integer format.

{
"exp": 1460192076
}

Acting on claims in the token

You can of course add extra claims in the claim section. Once the token is validated, the claims you include will be passed as headers to a downstream resource. Since the token has been validated by Caddy, you can be assured that these headers represent valid claims from your token. For example, if you include the following claims in your token:

{
"user": "test",
"role": "admin",
"logins": 10
}

The following headers will be added to the request that is proxied to your application:

Token-Claim-User: test
Token-Claim-Role: admin
Token-Claim-Logins: 10

Token claims will always be converted to a string. If you expect your claim to be another type, remember to convert it back before you use it.

Caveats

JWT validation depends only on validating the correct signature and that the token is unexpired. You can also set the nbf field to prevent validation before a certain timestamp. Other fields in the specification, such as aud, iss, sub, iat, and jti will not affect the validation step.