BREAKING CHANGES:* Version 3.0.0 is here. It includes a lot of changes including a few that break the API. We've tried to break as few things as possible, so there should just be a few type signature changes. A full list of breaking changes is available in
MIGRATION_GUIDE.md for more information on updating your code.
NOTICE: A vulnerability in JWT was recently published. As this library doesn't force users to validate the
alg is what they expected, it's possible your usage is effected. There will be an update soon to remedy this, and it will likey require backwards-incompatible changes to the API. In the short term, please make sure your implementation verifies the
alg is what you expect.
What the heck is a JWT?
JWT.io has a great introduction to JSON Web Tokens.
In short, it's a signed JSON object that does something useful (for example, authentication). It's commonly used for
Bearer tokens in Oauth 2. A token is made of three parts, separated by
.'s. The first two parts are JSON objects, that have been base64url encoded. The last part is the signature, encoded the same way.
The first part is called the header. It contains the necessary information for verifying the last part, the signature. For example, which encryption method was used for signing and what key was used.
The part in the middle is the interesting bit. It's called the Claims and contains the actual stuff you care about. Refer to the RFC for information about reserved keys and the proper way to add your own.
What's in the box?
This library supports the parsing and verification as well as the generation and signing of JWTs. Current supported signing algorithms are HMAC SHA, RSA, RSA-PSS, and ECDSA, though hooks are present for adding your own.
See the project documentation for examples of usage:
- Simple example of parsing and validating a token
- Simple example of building and signing a token
- Directory of Examples
This library publishes all the necessary components for adding your own signing methods. Simply implement the
SigningMethod interface and register a factory method using
Here's an example of an extension that integrates with the Google App Engine signing tools: https://github.com/someone1/gcp-jwt-go
This library was last reviewed to comply with RTF 7519 dated May 2015 with a few notable differences:
- In order to protect against accidental use of Unsecured JWTs, tokens using
alg=nonewill only be accepted if the constant
jwt.UnsafeAllowNoneSignatureTypeis provided as the key.
Project Status & Versioning
This library is considered production ready. Feedback and feature requests are appreciated. The API should be considered stable. There should be very few backwards-incompatible changes outside of major version updates (and only with good reason).
While we try to make it obvious when we make breaking changes, there isn't a great mechanism for pushing announcements out to users. You may want to use this alternative package include:
gopkg.in/dgrijalva/jwt-go.v2. It will do the right thing WRT semantic versioning.
Signing vs Encryption
A token is simply a JSON object that is signed by its author. this tells you exactly two things about the data:
- The author of the token was in the possession of the signing secret
- The data has not been modified since it was signed
It's important to know that JWT does not provide encryption, which means anyone who has access to the token can read its contents. If you need to protect (encrypt) the data, there is a companion spec,
JWE, that provides this functionality. JWE is currently outside the scope of this library.
Choosing a Signing Method
There are several signing methods available, and you should probably take the time to learn about the various options before choosing one. The principal design decision is most likely going to be symmetric vs asymmetric.
Symmetric signing methods, such as HSA, use only a single secret. This is probably the simplest signing method to use since any
byte can be used as a valid secret. They are also slightly computationally faster to use, though this rarely is enough to matter. Symmetric signing methods work the best when both producers and consumers of tokens are trusted, or even the same system. Since the same secret is used to both sign and validate tokens, you can't easily distribute the key for validation.
Asymmetric signing methods, such as RSA, use different keys for signing and verifying tokens. This makes it possible to produce tokens with a private key, and allow any consumer to access the public key for verification.
JWT and OAuth
It's worth mentioning that OAuth and JWT are not the same thing. A JWT token is simply a signed JSON object. It can be used anywhere such a thing is useful. There is some confusion, though, as JWT is the most common type of bearer token used in OAuth2 authentication.
Without going too far down the rabbit hole, here's a description of the interaction of these technologies:
- OAuth is a protocol for allowing an identity provider to be separate from the service a user is logging in to. For example, whenever you use Facebook to log into a different service (Yelp, Spotify, etc), you are using OAuth.
- OAuth defines several options for passing around authentication data. One popular method is called a "bearer token". A bearer token is simply a string that should only be held by an authenticated user. Thus, simply presenting this token proves your identity. You can probably derive from here why a JWT might make a good bearer token.
- Because bearer tokens are used for authentication, it's important they're kept secret. This is why transactions that use bearer tokens typically happen over SSL.
Documentation can be found on godoc.org.
The command line utility included in this project (cmd/jwt) provides a straightforward example of token creation and parsing as well as a useful tool for debugging your own integration. You'll also find several implementation examples in to documentation.