How to use the oidcmsg Message class

Basic usage

An oidcmsg oidcmsg.message.Message instance have some functionality common with Python dictionaries. So you can do things like assign values to a key:

>>> from oidcmsg.message import Message
>>> msg = Message()
>>> msg['key'] = 'value'

And you can read a value assigned to a key:

>>> from oidcmsg.message import Message
>>> msg = Message()
>>> msg['key'] = 'value'
>>> val = msg['key']
>>> print(val)
value

oidcmsg.message.Message also supports other dictionary methods:

>>> from oidcmsg.message import Message
>>> msg = Message()
>>> msg['key'] = 'value'
>>> list(msg.keys())
['key']
>>> list(msg.items())
[('key', 'value')]
>>> 'key' in msg
True
>>> print(msg)
{'key': 'value'}

>>> msg['another'] = 2
>>> msg.keys()
dict_keys(['another', 'key'])
>>> msg.values()
dict_values([2, 'value'])
>>> del msg['key']
>>> print(msg)
{'another': 2}

Like a dictionary one can also do:

>>> from oidcmsg.message import Message
>>> msg = Message(key='value', other=6)
>>> print(msg)
{'other': 6, 'key': 'value'}

Serialization/deserialization

Since instances of oidcmsg.message.Message will be used in an environment where information are to be sent over a wire it must be possible to serialize the information in such an instance to a format that can be transmitted over-the-wire.

Because of this a number of method has been added to support serialization to and deserialization from a number of representations that are used in the OAuth2 and OIDC protocol exchange.

The format supported are:

  • JSON
  • urlencoded
  • Jason Web Token (JWT) signed and/or encrypted.

An example using url encoding:

>>> from oidcmsg.message import Message
>>> msg = Message()
>>> msg['key'] = 'value'
>>> msg['another'] = 2
>>> msg.to_urlencoded()
'another=2&key=value'

>>> urlenc = msg.to_urlencoded()
>>> recmsg = Message().from_urlencoded(urlenc)
>>> print(recmsg)
{'key': 'value', 'another': '2'}

Same thing using JSON:

>>> from oidcmsg.message import Message
>>> msg = Message(key='value', another=2)
>>> msg.to_urlencoded()
'another=2&key=value'

>>> json_msg = msg.to_json()
>>> recmsg = Message().from_json(json_msg)
>>> print(recmsg)
{'another': 2, 'key': 'value'}

Regarding signed Jason Web Tokens we need a key so I create a simple symmetric one:

>>> from oidcmsg.message import Message
>>> from cryptojwt.jwk.hmac import SYMKey
>>> msg = Message(key='value', another=2)
>>> keys = [SYMKey(key="A1B2C3D4")]
>>> jws = msg.to_jwt(keys, "HS256")
>>> print(jws)
eyJhbGciOiJIUzI1NiJ9.eyJrZXkiOiAidmFsdWUiLCAiYW5vdGhlciI6IDJ9.-yoKjzgRxQu0KqyH-6wRNB8g6W7PSu2cbHRguCjc18k
>>> recv = Message().from_jwt(jws, key=keys)
>>> print(recv)
{'another': 2, 'key': 'value'}

Verifying the message content

A protocol specification would not be anything if it didn’t specify what a message is supposed to look like. Which attributes that can occur in a message and what type of values the attributes could have. And in some extreme case the specification can also specify the exact values that a specific attribute can have.

The OAuth2 and OpenID Connect specifications does all that. But both of them also states that extra attributes can always occur and should be allowed.

A oidcmsg.message.Message class ínstance can deal with this.

Let’s take the basic error response as an example. This message is defined thus in oidcmsg:

class ErrorResponse(Message):
c_param = {"error": SINGLE_REQUIRED_STRING,
           "error_description": SINGLE_OPTIONAL_STRING,
           "error_uri": SINGLE_OPTIONAL_STRING}

What this means is that error must have a string value and that error_description and error_uri may have values and if so single string values.

What does this look like then:

>>> from oidcmsg.oauth2 import ErrorResponse
>>> err = ErrorResponse(error='invalid_request')
>>> err.verify()
True

So with error defined the verify method will evaluate to True. If we forget to provide the error attribute:

>>> err = ErrorResponse(error_description='Some strange error')
>>> err.verify()
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/oidcmsg-0.1.0-py3.6.egg/oidcmsg/message.py", line 617, in verify
    val = self._dict[attribute]
KeyError: 'error'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages/oidcmsg-0.1.0-py3.6.egg/oidcmsg/message.py", line 620, in verify
    raise MissingRequiredAttribute("%s" % attribute)
oidcmsg.exception.MissingRequiredAttribute: Missing required attribute 'error'

an exception will be raised.

If you provide extra attributes, that is OK but those attributes can not be verified.

>>> from oidcmsg.oauth2 import ErrorResponse
>>> err = ErrorResponse(error='invalid_request', error_code=500)
>>> err.verify()
True
>>> print(err)
{'error': 'invalid_request', 'error_code': 500}