path: root/README.md

# PyJWT

[![build-status-image]][travis]
[![pypi-version]][pypi]

A Python implementation of [JSON Web Token draft 01][jwt-draft-01] originally written by [@progrium][progrium].

## Installing

```
$ pip install PyJWT
```

**A Note on Dependencies**:

RSA and ECDSA signatures depend on the cryptography package. If you plan on
using any of those algorithms, you'll need to install it as well.

```
$ pip install cryptography
```

## Usage

```python
import jwt
jwt.encode({'some': 'payload'}, 'secret')
```

Additional headers may also be specified.

```python
jwt.encode({'some': 'payload'}, 'secret', headers={'kid': '230498151c214b788dd97f22b85410a5'})
```

Note the resulting JWT will not be encrypted, but verifiable with a secret key.

```python
jwt.decode('someJWTstring', 'secret')
```

If the secret is wrong, it will raise a `jwt.DecodeError` telling you as such.
You can still get the payload by setting the `verify` argument to `False`.

```python
jwt.decode('someJWTstring', verify=False)
```

The `decode()` function can raise other exceptions, e.g. for invalid issuer or audience (see below). All exceptions that signify that the token is invalid extend from the base `InvalidTokenError` exception class, so applications can use this approach to catch any issues relating to invalid tokens:

```python
try:
    payload = jwt.decode('someJWTstring')
except jwt.InvalidTokenError:
    pass  # do something sensible here, e.g. return HTTP 403 status code
```


## Algorithms

The JWT spec supports several algorithms for cryptographic signing. This library
currently supports:

* HS256 - HMAC using SHA-256 hash algorithm (default)
* HS384 - HMAC using SHA-384 hash algorithm
* HS512 - HMAC using SHA-512 hash algorithm
* ES256 - ECDSA signature algorithm using SHA-256 hash algorithm
* ES384 - ECDSA signature algorithm using SHA-384 hash algorithm
* ES512 - ECDSA signature algorithm using SHA-512 hash algorithm
* RS256 - RSASSA-PKCS1-v1_5 signature algorithm using SHA-256 hash algorithm
* RS384 - RSASSA-PKCS1-v1_5 signature algorithm using SHA-384 hash algorithm
* RS512 - RSASSA-PKCS1-v1_5 signature algorithm using SHA-512 hash algorithm

Change the algorithm with by setting it in encode:

```python
jwt.encode({'some': 'payload'}, 'secret', 'HS512')
```

When using the RSASSA-PKCS1-v1_5 algorithms, the `key` argument in both
`jwt.encode()` and `jwt.decode()` (`"secret"` in the examples) is expected to
be either an RSA public or private key in PEM format.

When using the ECDSA algorithms, the `key` argument is expected to
be an Elliptic Curve private key or an Elliptic Curve public
key in PEM format.

## Tests

You can run tests from the project root after cloning with:

```
$ python tests/test_jwt.py
```

## Support of reserved claim names

JSON Web Token defines some reserved claim names and defines how they should be
used. PyJWT supports these reserved claim names:

 - "exp" (Expiration Time) Claim
 - "nbf" (Not Before Time) Claim
 - "iss" (Issuer) Claim
 - "aud" (Audience) Claim

### Expiration Time Claim

From [draft 01 of the JWT spec][reserved-claimname]:

> The exp (expiration time) claim identifies the expiration time on or after
> which the JWT MUST NOT be accepted for processing. The processing of the exp
> claim requires that the current date/time MUST be before the expiration
> date/time listed in the exp claim. Implementers MAY provide for some small
> leeway, usually no more than a few minutes, to account for clock skew. Its
> value MUST be a number containing an IntDate value. Use of this claim is
> OPTIONAL.

You can pass the expiration time as a UTC UNIX timestamp (an int) or as a
datetime, which will be converted into an int. For example:

```python
jwt.encode({'exp': 1371720939}, 'secret')

jwt.encode({'exp': datetime.utcnow()}, 'secret')
```

Expiration time is automatically verified in `jwt.decode()` and raises
`jwt.ExpiredSignatureError` if the expiration time is in the past:

```python
import jwt

try:
    jwt.decode('JWT_STRING', 'secret')
except jwt.ExpiredSignatureError:
    # Signature has expired
```

Expiration time will be compared to the current UTC time (as given by
`timegm(datetime.utcnow().utctimetuple())`), so be sure to use a UTC timestamp
or datetime in encoding.

You can turn off expiration time verification with the `verify_expiration` argument.

PyJWT also supports the leeway part of the expiration time definition, which
means you can validate a expiration time which is in the past but not very far.
For example, if you have a JWT payload with a expiration time set to 30 seconds
after creation but you know that sometimes you will process it after 30 seconds,
you can set a leeway of 10 seconds in order to have some margin:

```python
import datetime
import time
import jwt

jwt_payload = jwt.encode({
    'exp': datetime.datetime.utcnow() + datetime.timedelta(seconds=30)
}, 'secret')

time.sleep(32)

# JWT payload is now expired
# But with some leeway, it will still validate
jwt.decode(jwt_payload, 'secret', leeway=10)
```

Instead of specifying the leeway as a number of seconds, a `datetime.timedelta` instance can be used. The last line in the example above is equivalent to:

```python
jwt.decode(jwt_payload, 'secret', leeway=datetime.timedelta(seconds=10))
```


### Not Before Time Claim

> The nbf (not before) claim identifies the time before which the JWT MUST NOT be accepted for processing. The processing of the nbf claim requires that the current date/time MUST be after or equal to the not-before date/time listed in the nbf claim. Implementers MAY provide for some small leeway, usually no more than a few minutes, to account for clock skew. Its value MUST be a number containing a NumericDate value. Use of this claim is OPTIONAL.

The `nbf` claim works similarly to the `exp` claim above.

```python
jwt.encode({'nbf': 1371720939}, 'secret')

jwt.encode({'nbf': datetime.utcnow()}, 'secret')
```

### Issuer Claim

> The iss (issuer) claim identifies the principal that issued the JWT. The processing of this claim is generally application specific. The iss value is a case-sensitive string containing a StringOrURI value. Use of this claim is OPTIONAL.

```python
import jwt


payload = {
    'some': 'payload',
    'iss': 'urn:foo'
}

token = jwt.encode(payload, 'secret')
decoded = jwt.decode(token, 'secret', issuer='urn:foo')
```

If the issuer claim is incorrect, `jwt.InvalidIssuerError` will be raised.


### Audience Claim

> The aud (audience) claim identifies the recipients that the JWT is intended for. Each principal intended to process the JWT MUST identify itself with a value in the audience claim. If the principal processing the claim does not identify itself with a value in the aud claim when this claim is present, then the JWT MUST be rejected. In the general case, the aud value is an array of case-sensitive strings, each containing a StringOrURI value. In the special case when the JWT has one audience, the aud value MAY be a single case-sensitive string containing a StringOrURI value. The interpretation of audience values is generally application specific. Use of this claim is OPTIONAL.

```python
import jwt


payload = {
    'some': 'payload',
    'aud': 'urn:foo'
}

token = jwt.encode(payload, 'secret')
decoded = jwt.decode(token, 'secret', audience='urn:foo')
```

If the audience claim is incorrect, `jwt.InvalidAudienceError` will be raised.


## License

MIT

[build-status-image]: https://secure.travis-ci.org/jpadilla/pyjwt.png?branch=master
[travis]: http://travis-ci.org/jpadilla/pyjwt?branch=master
[pypi-version]: https://pypip.in/version/pyjwt/badge.svg
[pypi]: https://pypi.python.org/pypi/pyjwt
[jwt-draft-01]: http://self-issued.info/docs/draft-jones-json-web-token-01.html
[progrium]: https://github.com/progrium
[reserved-claimname]: http://self-issued.info/docs/draft-jones-json-web-token-01.html#ReservedClaimName