"""
Amazon Web Services version 4 authentication for the Python `Requests`_
library.

.. _Requests: https://github.com/kennethreitz/requests

Features
--------
* Requests authentication for all AWS services that support AWS auth v4
* Independent signing key objects
* Automatic regeneration of keys when scope date boundary is passed
* Support for STS temporary credentials

Implements header-based authentication, GET URL parameter and POST parameter
authentication are not supported.

Supported Services
------------------
This package has been tested as working against:

AppStream, Auto-Scaling, CloudFormation, CloudFront, CloudHSM, CloudSearch,
CloudTrail, CloudWatch Monitoring, CloudWatch Logs, CodeDeploy, Cognito
Identity, Cognito Sync, Config, DataPipeline, Direct Connect, DynamoDB, Elastic
Beanstalk, ElastiCache, EC2, EC2 Container Service, Elastic Load Balancing,
Elastic MapReduce, ElasticSearch, Elastic Transcoder, Glacier, Identity and
Access Management (IAM), Key Management Service (KMS), Kinesis, Lambda,
Opsworks, Redshift, Relational Database Service (RDS), Route 53, Simple Storage
Service (S3), Simple Notification Service (SNS), Simple Queue Service (SQS),
Storage Gateway, Security Token Service (STS)

The following services do not support AWS auth version 4 and are not usable
with this package:

Simple Email Service (SES), Simple Workflow Service (SWF), Import/Export,
SimpleDB, DevPay, Mechanical Turk

The AWS Support API has not been tested as it requires a premium subscription.

Installation
------------
Install via pip:

.. code-block:: bash

    $ pip install requests-aws4auth

requests-aws4auth requires the `Requests`_ library by Kenneth Reitz.

requests-aws4auth is tested on Python 2.7 and 3.3 and up.

Behaviour changes in 0.8
------------------------
Version 0.8 introduces request date checking and automatic key regeneration
behaviour as default. This has implications for sharing authentication objects
between threads, and for storage of secret keys. See the relevant sections
below for details. See also the discussion in `GitHub issue #10`_.

.. _GitHub issue #10: https://github.com/sam-washington/requests-aws4auth/issues/10

Basic usage
-----------
.. code-block:: python

    >>> import requests
    >>> from requests_aws4auth import AWS4Auth
    >>> endpoint = 'http://s3-eu-west-1.amazonaws.com'
    >>> auth = AWS4Auth('<ACCESS ID>', '<ACCESS KEY>', 'eu-west-1', 's3')
    >>> response = requests.get(endpoint, auth=auth)
    >>> response.text
    <?xml version="1.0" encoding="UTF-8"?>
        <ListAllMyBucketsResult xmlns="http://s3.amazonaws.com/doc/2006-03-01">
            <Owner>
            <ID>bcaf1ffd86f461ca5fb16fd081034f</ID>
            <DisplayName>webfile</DisplayName>
            ...

This example would list your buckets in the ``eu-west-1`` region of the Amazon
S3 service.

STS Temporary Credentials
-------------------------
.. code-block:: python

    >>> from requests_aws4auth import AWS4Auth
    >>> auth = AWS4Auth('<ACCESS ID>', '<ACCESS KEY>', 'eu-west-1', 's3',
                        session_token='<SESSION TOKEN>')
    ...

This example shows how to construct an AWS4Auth object for use with STS
temporary credentials. The ``x-amz-security-token`` header is added with
the session token. Temporary credential timeouts are not managed -- in
case the temporary credentials expire, they need to be re-generated and
the AWS4Auth object re-constructed with the new credentials.

Date handling
-------------
If an HTTP request to be authenticated contains a ``Date`` or ``X-Amz-Date``
header, AWS will only accept the authorised request if the date in the header
matches the scope date of the signing key (see the `AWS REST API date docs`_).

.. _AWS REST API date docs: http://docs.aws.amazon.com/general/latest/gr/sigv4-date-handling.html).

From version 0.8 of requests-aws4auth, if the header date does not match the
scope date, an ``AWS4Auth`` instance will automatically regenerate its signing
key, using the same scope parameters as the previous key except for the date,
which will be changed to match the request date. If a request does not include
a date, the current date is added to the request in an ``X-Amz-Date`` header,
and the signing key is regenerated if this differs from the scope date.

This means that ``AWS4Auth`` now extracts and parses dates from the values of
``X-Amz-Date`` and ``Date`` headers. Supported date formats are:

* RFC 7231 (e.g. Mon, 09 Sep 2011 23:36:00 GMT)
* RFC 850 (e.g. Sunday, 06-Nov-94 08:49:37 GMT)
* C time (e.g. Wed Dec 4 00:00:00 2002)
* Amz-Date format (e.g. 20090325T010101Z)
* ISO 8601 / RFC 3339 (e.g. 2009-03-25T10:11:12.13-01:00)

If either header is present but ``AWS4Auth`` cannot extract a date because all
present date headers are in an unrecognisable format, ``AWS4Auth`` will delete
any ``X-Amz-Date`` and ``Date`` headers present and replace with a single
``X-Amz-Date`` header containing the current date. This behaviour can be
modified using the ``raise_invalid_date`` keyword argument of the ``AWS4Auth``
constructor.

Automatic key regeneration
--------------------------
If you do not want the signing key to be automatically regenerated when a
mismatch between the request date and the scope date is encountered, use the
alternative ``StrictAWS4Auth`` class, which is identical to ``AWS4Auth`` except
that upon encountering a date mismatch it just raises a ``DateMismatchError``.
You can also use the ``PassiveAWS4Auth`` class, which mimics the ``AWS4Auth``
behaviour prior to version 0.8 and just signs and sends the request, whether
the date matches or not. In this case it is up to the calling code to handle an
authentication failure response from AWS caused by the date mismatch.

Secret key storage
------------------
To allow automatic key regeneration, the secret key is stored in the
``AWS4Auth`` instance, in the signing key object. If you do not want this to
occur, instantiate the instance using an ``AWS4Signing`` key which was created
with the store_secret_key parameter set to False:

.. code-block:: python

    >>> sig_key = AWS4SigningKey(secret_key, region, service, date, False)
    >>> auth = StrictAWS4Auth(access_id, sig_key)

The ``AWS4Auth`` class will then raise a ``NoSecretKeyError`` when it attempts
to regenerate its key. A slightly more conceptually elegant way to handle this
is to use the alternative ``StrictAWS4Auth`` class, again instantiating it with
an ``AWS4SigningKey`` instance created with ``store_secret_key = False``.

Multithreading
--------------
If you share ``AWS4Auth`` (or even ``StrictAWS4Auth``) instances between
threads you are likely to encounter problems. Because ``AWS4Auth`` instances
may unpredictably regenerate their signing key as part of signing a request,
threads using the same instance may find the key changed by another thread
halfway through the signing process, which may result in undefined behaviour.

It may be possible to rig up a workable instance sharing mechanism using
locking primitives and the ``StrictAWS4Auth`` class, however this poor author
can't think of a scenario which works safely yet doesn't suffer from at some
point blocking all threads for at least the duration of an HTTP request, which
could be several seconds. If several requests come in in close succession which
all require key regenerations then the system could be forced into serial
operation for quite a length of time.

In short, it's probably best to create a thread-local instance of ``AWS4Auth``
for each thread that needs to do authentication.

API reference
-------------
See the doctrings in ``aws4auth.py`` and ``aws4signingkey.py``.

Testing
-------
A test suite is included in the test folder.

The package passes all tests in the AWS auth v4 `test_suite`_, and contains
tests against the supported live services. See docstrings in
``test/requests_aws4auth_test.py`` for details about running the tests.

Connection parameters are included in the tests for the AWS Support API, should
you have access and want to try it. The documentation says it supports auth v4
so it should work if you have a subscription. Do pass on your results!

.. _test_suite: http://docs.aws.amazon.com/general/latest/gr/signature-v4-test-suite.html

Unsupported AWS features / todo
-------------------------------
* Currently does not support Amazon S3 chunked uploads
* Tests for new AWS services
* Requires Requests library to be present even if only using
* Coherent documentation

"""

# Licensed under the MIT License:
# http://opensource.org/licenses/MIT


from .aws4auth import AWS4Auth, StrictAWS4Auth, PassiveAWS4Auth
from .aws4signingkey import AWS4SigningKey
from .exceptions import RequestsAws4AuthException, DateMismatchError, NoSecretKeyError
del aws4auth
del aws4signingkey
del exceptions

__version__ = '0.9'
