ska 0.2

Signing (HTTP) requests using symmetric-key algorithm.

Symmetric-key algorithm encryption. Lets you easily generate signatures for signing (HTTP) requests. Allows you to validate signed requests and identify possible validation errors.

Key concepts

Host and server share the Secret Key, which is used to sign requests. Secret key is never sent around.

Each HTTP request is signed on the client side using the shared Secret Key and as an outcome produces the triple (signature, auth_user, valid_until) which are used to sign the requests.

• signature (str): Signature generated.

• auth_user (str): User making the request. Can be anything.

• valid_until (float|str): Signature expiration time (Unix timestamp).

On the server side, HTTP request is validated using the shared Secret Key. It’s being checked whether signature is valid and not expired.

Installation

$ pip install ska

Usage examples

Basic usage

Client side

Signing URLs is as simple as follows.

Required imports.

>>> from ska import sign_url

Producing a signed URL.

>>> signed_url = sign_url(
>>>     auth_user='user', secret_key='your-secret_key', url='http://e.com/api/'
>>> )
http://e.com/api/?valid_until=1378045287.0&auth_user=user&signature=YlZpLFsjUKBalL4x5trhkeEgqE8%3D

Default lifetime of a signature is 10 minutes (600 seconds). If you want it to be different, provide a lifetime argument to sign_url function.

Default name of the GET param holding the generated signature value is signature. If you want it to be different, provide a signature_param argument to sign_url function.

Default name of the GET param holding the auth_user value is auth_user. If you want it to be different, provide a auth_user_param argument to sign_url function.

Default name of the GET param holding the valid_until value is valid_until. If you want it to be different, provide a valid_until_param argument to sign_url function.

With all customisations, it would look as follows.

>>> signed_url = sign_url(
>>>     auth_user='user', secret_key='your-secret_key', lifetime=120,
>>>     url='http://e.com/api/', signature_param='signature',
>>>     auth_user_param='auth_user', valid_until_param='valid_until'
>>> )

You may now proceed with the signed URL request. If you use the famous requests library, it would be as follows.

>>> import requests
>>> requests.get(signed_url)

If you for some reason prefer a lower level implementation, read the same section in the Advanced usage chapter.

Server side

Validating the signed request data is as simple as follows

Required imports.

>>> from ska import validate_signed_request_data

Validating the signed request data. Note, that data value is expected to be a dictionary; request.GET is given as an example. It will most likely vary from what’s used in your framework (unless you use Django).

>>> validation_result = validate_signed_request_data(
>>>     data = request.GET, # Note, that ``request.GET`` is given as example.
>>>     secret_key = 'your-secret_key'
>>> )

The validate_signed_request_data produces a ska.SignatureValidationResult object, which holds the following data:

• result (bool): True if data is valid. False otherwise.

• reason (list): List of strings, indicating validation errors. Empty list in case if result is True.

Default name of the GET param holding the signature value is signature. If you want it to be different, provide a signature_param argument to validate_signed_request_data function.

Default name of the GET param holding the auth_user value is auth_user. If you want it to be different, provide a auth_user_param argument to validate_signed_request_data function.

Default name of the GET param holding the valid_until value is valid_until. If you want it to be different, provide a valid_until_param argument to validate_signed_request_data function.

With all customisations, it would look as follows.

>>> validation_result = validate_signed_request_data(
>>>     data = request.GET,
>>>     secret_key = 'your-secret_key',
>>>     signature_param='signature',
>>>     auth_user_param='auth_user', \
>>>     valid_until_param='valid_until'
>>> )

If you for some reason prefer a lower level implementation, read the same section in the Advanced usage chapter.

Advanced usage (low-level)

Client side

Required imports.

>>> from ska import Signature, RequestHelper

Generate a signature.

>>> signature = Signature.generate_signature(
>>>     auth_user = 'user',
>>>     secret_key = 'your-secret-key'
>>>     )

Default lifetime of a signature is 10 minutes (600 seconds). If you want it to be different, provide a lifetime argument to generate_signature method.

>>> signature = Signature.generate_signature(
>>>     auth_user = 'user',
>>>     secret_key = 'your-secret-key',
>>>     lifetime = 120 # Signatre lifetime set to 120 seconds.
>>>     )

Your endpoint operates with certain param names and you need to wrap generated signature params into the URL. In order to have the job done in an easy way, create a request helper. Feed names of the GET params to the request helper and let it make a signed endpoint URL for you.

>>> request_helper = RequestHelper(
>>>     signature_param = 'signature',
>>>     auth_user_param = 'auth_user',
>>>     valid_until_param = 'valid_until'
>>> )

Append signature params to the endpoint URL.

>>> signed_url = request_helper.signature_to_url(
>>>     signature = signature,
>>>     endpoint_url = 'http://e.com/api/'
>>> )
http://e.com/api/?valid_until=1378045287.0&auth_user=user&signature=YlZpLFsjUKBalL4x5trhkeEgqE8%3D

Make a request.

>>> import requests
>>> r = requests.get(signed_url)

Server side

Required imports.

>>> from ska import RequestHelper

Create a request helper. Your endpoint operates with certain param names. In order to have the job done in an easy way, we feed those params to the request helper and let it extract data from signed request for us.

>>> request_helper = RequestHelper(
>>>     signature_param = 'signature',
>>>     auth_user_param = 'auth_user',
>>>     valid_until_param = 'valid_until'
>>> )

Validate the request data. Note, that request.GET is given just as an example.

>>> validation_result = request_helper.validate_request_data(
>>>     data = request.GET,
>>>     secret_key = 'your-secret-key'
>>> )

Your implementation further depends on you, but may look as follows.

>>> if validation_result.result:
>>>     # Validated, proceed further
>>>     # ...
>>> else:
>>>     # Validation not passed.
>>>     raise Http404(validation_result.reason)

You can also just validate the signature by calling validate_signature method of the ska.Signature.

>>> Signature.validate_signature(
>>>     signature = 'EBS6ipiqRLa6TY5vxIvZU30FpnM=',
>>>     auth_user = 'user',
>>>     secret_key = 'your-secret-key',
>>>     valid_until = '1377997396.0'
>>>     )

License

GPL 2.0/LGPL 2.1

Support

For any issues contact me at the e-mail given in the Author section.

Author

Artur Barseghyan <[e-mail]>