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JWT Go Reference

Package jwt implements JSON Web Tokens as described in RFC7519.

  • Convenience methods for oft-used keys ("aud", "sub", "iss", etc)
  • Convenience functions to extract/parse from http.Request, http.Header, url.Values
  • Ability to Get/Set arbitrary keys
  • Conversion to and from JSON
  • Generate signed tokens
  • Verify signed tokens
  • Extra support for OpenID tokens via github.com/lestrrat-go/jwx/jwt/openid

How-to style documentation can be found in the docs directory.

More examples are located in the examples directory (jwt_example_test.go)

SYNOPSIS

Verify a signed JWT

  token, err := jwt.Parse(payload, jwt.WithKeySet(keyset))
  if err != nil {
    fmt.Printf("failed to parse payload: %s\n", err)
  }

Token Usage

func ExampleJWT() {
  const aLongLongTimeAgo = 233431200

  t := jwt.New()
  t.Set(jwt.SubjectKey, `https://github.com/lestrrat-go/jwx/jwt`)
  t.Set(jwt.AudienceKey, `Golang Users`)
  t.Set(jwt.IssuedAtKey, time.Unix(aLongLongTimeAgo, 0))
  t.Set(`privateClaimKey`, `Hello, World!`)

  buf, err := json.MarshalIndent(t, "", "  ")
  if err != nil {
    fmt.Printf("failed to generate JSON: %s\n", err)
    return
  }

  fmt.Printf("%s\n", buf)
  fmt.Printf("aud -> '%s'\n", t.Audience())
  fmt.Printf("iat -> '%s'\n", t.IssuedAt().Format(time.RFC3339))
  if v, ok := t.Get(`privateClaimKey`); ok {
    fmt.Printf("privateClaimKey -> '%s'\n", v)
  }
  fmt.Printf("sub -> '%s'\n", t.Subject())

  key, err := rsa.GenerateKey(rand.Reader, 2048)
  if err != nil {
    log.Printf("failed to generate private key: %s", err)
    return
  }

  {
    // Signing a token (using raw rsa.PrivateKey)
    signed, err := jwt.Sign(t, jwa.RS256, key)
    if err != nil {
      log.Printf("failed to sign token: %s", err)
      return
    }
    _ = signed
  }

  {
    // Signing a token (using JWK)
    jwkKey, err := jwk.New(key)
    if err != nil {
      log.Printf("failed to create JWK key: %s", err)
      return
    }

    signed, err := jwt.Sign(t, jwa.RS256, jwkKey)
    if err != nil {
      log.Printf("failed to sign token: %s", err)
      return
    }
    _ = signed
  }
}

OpenID Claims

jwt package can work with token types other than the default one. For OpenID claims, use the token created by openid.New(), or use the jwt.WithToken(openid.New()). If you need to use other specialized claims, use jwt.WithToken() to specify the exact token type

func Example_openid() {
  const aLongLongTimeAgo = 233431200

  t := openid.New()
  t.Set(jwt.SubjectKey, `https://github.com/lestrrat-go/jwx/jwt`)
  t.Set(jwt.AudienceKey, `Golang Users`)
  t.Set(jwt.IssuedAtKey, time.Unix(aLongLongTimeAgo, 0))
  t.Set(`privateClaimKey`, `Hello, World!`)

  addr := openid.NewAddress()
  addr.Set(openid.AddressPostalCodeKey, `105-0011`)
  addr.Set(openid.AddressCountryKey, `日本`)
  addr.Set(openid.AddressRegionKey, `東京都`)
  addr.Set(openid.AddressLocalityKey, `港区`)
  addr.Set(openid.AddressStreetAddressKey, `芝公園 4-2-8`)
  t.Set(openid.AddressKey, addr)

  buf, err := json.MarshalIndent(t, "", "  ")
  if err != nil {
    fmt.Printf("failed to generate JSON: %s\n", err)
    return
  }
  fmt.Printf("%s\n", buf)

  t2, err := jwt.Parse(buf, jwt.WithToken(openid.New()))
  if err != nil {
    fmt.Printf("failed to parse JSON: %s\n", err)
    return
  }
  if _, ok := t2.(openid.Token); !ok {
    fmt.Printf("using jwt.WithToken(openid.New()) creates an openid.Token instance")
    return
  }
}

FAQ

Why is jwt.Token an interface?

In this package, jwt.Token is an interface. This is not an arbitrary choice: there are actual reason for the type being an interface.

We understand that if you are migrating from another library this may be a deal breaker, but we hope you can at least appreciate the fact that this was not done arbitrarily, and that there were real technical trade offs that were evaluated.

No uninitialized tokens

First and foremost, by making it an interface, you cannot use an uninitialized token:

var token1 jwt.Token // this is nil, you can't just start using this
if err := json.Unmarshal(data, &token1); err != nil { // so you can't do this
   ...
}

// But you _can_ do this, and we _want_ you to do this so the object is properly initialized
token2 = jwt.New()
if err := json.Unmarshal(data, &token2); err != nil { // actually, in practice you should use jwt.Parse()
   ....
}

But why does it need to be initialized?

There are several reasons, but one of the reasons is that I'm using a sync.Mutex to avoid races. We want this to be properly initialized.

The other reason is that we support custom claims out of the box. The map[string]interface{} container is initialized during new. This is important when checking for equality using reflect-y methods (akin to reflect.DeepEqual), because if you allowed zero values, you could end up with "empty" tokens, that actually differ. Consider the following:

// assume jwt.Token was s struct, not an interface
token1 := jwt.Token{ privateClaims: make(map[string]interface{}) }
token2 := jwt.Token{ privateClaims: nil }

These are semantically equivalent, but users would need to be aware of this difference when comparing values. By forcing the user to use a constructor, we can force a uniform empty state.

Standard way to store values

Unlike some other libraries, this library allows you to store standard claims and non-standard claims in the same token.

You want to store standard claims in a properly typed field, which we do for fields like "iss", "nbf", etc. But for non-standard claims, there is just no way of doing this, so we have to use a container like map[string]interface{}

This means that if you allow direct access to these fields via a struct, you will have two different ways to access the claims, which is confusing:

tok.Issuer = ...
tok.PrivateClaims["foo"] = ...

So we want to hide where this data is stored, and use a standard method like Set() and Get() to store all the values. At this point you are effectively going to hide the implementation detail from the user, so you end up with a struct like below, which is fundamentally not so different from providing just an interface{}:

type Token struct {
  // unexported fields
}

func (tok *Token) Set(...) { ... }

Use of pointers to store values

We wanted to differentiate the state between a claim being uninitialized, and a claim being initialized to empty.

So we use pointers to store values:

type stdToken struct {
  ....
  issuer *string // if nil, uninitialized. if &(""), initialized to empty
}

This is fine for us, but we doubt that this would be something users would want to do. This is a subtle difference, but cluttering up the API with slight variations of the same type (i.e. pointers vs non-pointers) seemed like a bad idea to us.

token.Issuer = &issuer // want to avoid this

token.Set(jwt.IssuerKey, "foobar") // so this is what we picked

This way users no longer need to care how the data is internally stored.

Allow more than one type of token through the same interface

dgrijalva/jwt-go does this in a different way, but we felt that it would be more intuitive for all tokens to follow a single interface so there is fewer type conversions required.

See the openid token for an example.