# Copyright (c) 2012-2013 Mitch Garnaat http://garnaat.org/
# Copyright 2012-2014 Amazon.com, Inc. or its affiliates. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License"). You
# may not use this file except in compliance with the License. A copy of
# the License is located at
#
# http://aws.amazon.com/apache2.0/
#
# or in the "license" file accompanying this file. This file is
# distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF
# ANY KIND, either express or implied. See the License for the specific
# language governing permissions and limitations under the License.
import base64
import datetime
from hashlib import sha256
from hashlib import sha1
import hmac
import logging
from email.utils import formatdate
from operator import itemgetter
import functools
import time
import calendar

from botocore.exceptions import NoCredentialsError
from botocore.utils import normalize_url_path, percent_encode_sequence
from botocore.compat import HTTPHeaders
from botocore.compat import quote, unquote, urlsplit, parse_qs
from botocore.compat import urlunsplit
from botocore.compat import encodebytes
from botocore.compat import six
from botocore.compat import json
from botocore.compat import MD5_AVAILABLE

logger = logging.getLogger(__name__)


EMPTY_SHA256_HASH = (
    'e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855')
# This is the buffer size used when calculating sha256 checksums.
# Experimenting with various buffer sizes showed that this value generally
# gave the best result (in terms of performance).
PAYLOAD_BUFFER = 1024 * 1024
ISO8601 = '%Y-%m-%dT%H:%M:%SZ'
SIGV4_TIMESTAMP = '%Y%m%dT%H%M%SZ'
SIGNED_HEADERS_BLACKLIST = [
    'expect',
    'user-agent'
]


class BaseSigner(object):
    REQUIRES_REGION = False

    def add_auth(self, request):
        raise NotImplementedError("add_auth")


class SigV2Auth(BaseSigner):
    """
    Sign a request with Signature V2.
    """

    def __init__(self, credentials):
        self.credentials = credentials

    def calc_signature(self, request, params):
        logger.debug("Calculating signature using v2 auth.")
        split = urlsplit(request.url)
        path = split.path
        if len(path) == 0:
            path = '/'
        string_to_sign = '%s\n%s\n%s\n' % (request.method,
                                           split.netloc,
                                           path)
        lhmac = hmac.new(self.credentials.secret_key.encode('utf-8'),
                         digestmod=sha256)
        pairs = []
        for key in sorted(params):
            # Any previous signature should not be a part of this
            # one, so we skip that particular key. This prevents
            # issues during retries.
            if key == 'Signature':
                continue
            value = six.text_type(params[key])
            pairs.append(quote(key.encode('utf-8'), safe='') + '=' +
                         quote(value.encode('utf-8'), safe='-_~'))
        qs = '&'.join(pairs)
        string_to_sign += qs
        logger.debug('String to sign: %s', string_to_sign)
        lhmac.update(string_to_sign.encode('utf-8'))
        b64 = base64.b64encode(lhmac.digest()).strip().decode('utf-8')
        return (qs, b64)

    def add_auth(self, request):
        # The auth handler is the last thing called in the
        # preparation phase of a prepared request.
        # Because of this we have to parse the query params
        # from the request body so we can update them with
        # the sigv2 auth params.
        if self.credentials is None:
            raise NoCredentialsError
        if request.data:
            # POST
            params = request.data
        else:
            # GET
            params = request.param
        params['AWSAccessKeyId'] = self.credentials.access_key
        params['SignatureVersion'] = '2'
        params['SignatureMethod'] = 'HmacSHA256'
        params['Timestamp'] = time.strftime(ISO8601, time.gmtime())
        if self.credentials.token:
            params['SecurityToken'] = self.credentials.token
        qs, signature = self.calc_signature(request, params)
        params['Signature'] = signature
        return request


class SigV3Auth(BaseSigner):
    def __init__(self, credentials):
        self.credentials = credentials

    def add_auth(self, request):
        if self.credentials is None:
            raise NoCredentialsError
        if 'Date' in request.headers:
            del request.headers['Date']
        request.headers['Date'] = formatdate(usegmt=True)
        if self.credentials.token:
            if 'X-Amz-Security-Token' in request.headers:
                del request.headers['X-Amz-Security-Token']
            request.headers['X-Amz-Security-Token'] = self.credentials.token
        new_hmac = hmac.new(self.credentials.secret_key.encode('utf-8'),
                            digestmod=sha256)
        new_hmac.update(request.headers['Date'].encode('utf-8'))
        encoded_signature = encodebytes(new_hmac.digest()).strip()
        signature = ('AWS3-HTTPS AWSAccessKeyId=%s,Algorithm=%s,Signature=%s' %
                     (self.credentials.access_key, 'HmacSHA256',
                      encoded_signature.decode('utf-8')))
        if 'X-Amzn-Authorization' in request.headers:
            del request.headers['X-Amzn-Authorization']
        request.headers['X-Amzn-Authorization'] = signature


class SigV4Auth(BaseSigner):
    """
    Sign a request with Signature V4.
    """
    REQUIRES_REGION = True

    def __init__(self, credentials, service_name, region_name):
        self.credentials = credentials
        # We initialize these value here so the unit tests can have
        # valid values.  But these will get overriden in ``add_auth``
        # later for real requests.
        self._region_name = region_name
        self._service_name = service_name

    def _sign(self, key, msg, hex=False):
        if hex:
            sig = hmac.new(key, msg.encode('utf-8'), sha256).hexdigest()
        else:
            sig = hmac.new(key, msg.encode('utf-8'), sha256).digest()
        return sig

    def headers_to_sign(self, request):
        """
        Select the headers from the request that need to be included
        in the StringToSign.
        """
        header_map = HTTPHeaders()
        split = urlsplit(request.url)
        for name, value in request.headers.items():
            lname = name.lower()
            if lname not in SIGNED_HEADERS_BLACKLIST:
                header_map[lname] = value
        if 'host' not in header_map:
            header_map['host'] = split.netloc
        return header_map

    def canonical_query_string(self, request):
        # The query string can come from two parts.  One is the
        # params attribute of the request.  The other is from the request
        # url (in which case we have to re-split the url into its components
        # and parse out the query string component).
        if request.params:
            return self._canonical_query_string_params(request.params)
        else:
            return self._canonical_query_string_url(urlsplit(request.url))

    def _canonical_query_string_params(self, params):
        l = []
        for param in sorted(params):
            value = str(params[param])
            l.append('%s=%s' % (quote(param, safe='-_.~'),
                                quote(value, safe='-_.~')))
        cqs = '&'.join(l)
        return cqs

    def _canonical_query_string_url(self, parts):
        canonical_query_string = ''
        if parts.query:
            # [(key, value), (key2, value2)]
            key_val_pairs = []
            for pair in parts.query.split('&'):
                key, _, value = pair.partition('=')
                key_val_pairs.append((key, value))
            sorted_key_vals = []
            # Sort by the key names, and in the case of
            # repeated keys, then sort by the value.
            for key, value in sorted(key_val_pairs):
                sorted_key_vals.append('%s=%s' % (key, value))
            canonical_query_string = '&'.join(sorted_key_vals)
        return canonical_query_string

    def canonical_headers(self, headers_to_sign):
        """
        Return the headers that need to be included in the StringToSign
        in their canonical form by converting all header keys to lower
        case, sorting them in alphabetical order and then joining
        them into a string, separated by newlines.
        """
        headers = []
        sorted_header_names = sorted(set(headers_to_sign))
        for key in sorted_header_names:
            value = ','.join(v.strip() for v in
                             sorted(headers_to_sign.get_all(key)))
            headers.append('%s:%s' % (key, value))
        return '\n'.join(headers)

    def signed_headers(self, headers_to_sign):
        l = ['%s' % n.lower().strip() for n in set(headers_to_sign)]
        l = sorted(l)
        return ';'.join(l)

    def payload(self, request):
        if request.body and hasattr(request.body, 'seek'):
            position = request.body.tell()
            read_chunksize = functools.partial(request.body.read,
                                               PAYLOAD_BUFFER)
            checksum = sha256()
            for chunk in iter(read_chunksize, b''):
                checksum.update(chunk)
            hex_checksum = checksum.hexdigest()
            request.body.seek(position)
            return hex_checksum
        elif request.body:
            # The request serialization has ensured that
            # request.body is a bytes() type.
            return sha256(request.body).hexdigest()
        else:
            return EMPTY_SHA256_HASH

    def canonical_request(self, request):
        cr = [request.method.upper()]
        path = self._normalize_url_path(urlsplit(request.url).path)
        cr.append(path)
        cr.append(self.canonical_query_string(request))
        headers_to_sign = self.headers_to_sign(request)
        cr.append(self.canonical_headers(headers_to_sign) + '\n')
        cr.append(self.signed_headers(headers_to_sign))
        if 'X-Amz-Content-SHA256' in request.headers:
            body_checksum = request.headers['X-Amz-Content-SHA256']
        else:
            body_checksum = self.payload(request)
        cr.append(body_checksum)
        return '\n'.join(cr)

    def _normalize_url_path(self, path):
        normalized_path = quote(normalize_url_path(path), safe='/~')
        return normalized_path

    def scope(self, request):
        scope = [self.credentials.access_key]
        scope.append(request.context['timestamp'][0:8])
        scope.append(self._region_name)
        scope.append(self._service_name)
        scope.append('aws4_request')
        return '/'.join(scope)

    def credential_scope(self, request):
        scope = []
        scope.append(request.context['timestamp'][0:8])
        scope.append(self._region_name)
        scope.append(self._service_name)
        scope.append('aws4_request')
        return '/'.join(scope)

    def string_to_sign(self, request, canonical_request):
        """
        Return the canonical StringToSign as well as a dict
        containing the original version of all headers that
        were included in the StringToSign.
        """
        sts = ['AWS4-HMAC-SHA256']
        sts.append(request.context['timestamp'])
        sts.append(self.credential_scope(request))
        sts.append(sha256(canonical_request.encode('utf-8')).hexdigest())
        return '\n'.join(sts)

    def signature(self, string_to_sign, request):
        key = self.credentials.secret_key
        k_date = self._sign(('AWS4' + key).encode('utf-8'),
                            request.context['timestamp'][0:8])
        k_region = self._sign(k_date, self._region_name)
        k_service = self._sign(k_region, self._service_name)
        k_signing = self._sign(k_service, 'aws4_request')
        return self._sign(k_signing, string_to_sign, hex=True)

    def add_auth(self, request):
        if self.credentials is None:
            raise NoCredentialsError
        datetime_now = datetime.datetime.utcnow()
        request.context['timestamp'] = datetime_now.strftime(SIGV4_TIMESTAMP)
        # This could be a retry.  Make sure the previous
        # authorization header is removed first.
        self._modify_request_before_signing(request)
        canonical_request = self.canonical_request(request)
        logger.debug("Calculating signature using v4 auth.")
        logger.debug('CanonicalRequest:\n%s', canonical_request)
        string_to_sign = self.string_to_sign(request, canonical_request)
        logger.debug('StringToSign:\n%s', string_to_sign)
        signature = self.signature(string_to_sign, request)
        logger.debug('Signature:\n%s', signature)

        self._inject_signature_to_request(request, signature)

    def _inject_signature_to_request(self, request, signature):
        l = ['AWS4-HMAC-SHA256 Credential=%s' % self.scope(request)]
        headers_to_sign = self.headers_to_sign(request)
        l.append('SignedHeaders=%s' % self.signed_headers(headers_to_sign))
        l.append('Signature=%s' % signature)
        request.headers['Authorization'] = ', '.join(l)
        return request

    def _modify_request_before_signing(self, request):
        if 'Authorization' in request.headers:
            del request.headers['Authorization']
        self._set_necessary_date_headers(request)
        if self.credentials.token:
            if 'X-Amz-Security-Token' in request.headers:
                del request.headers['X-Amz-Security-Token']
            request.headers['X-Amz-Security-Token'] = self.credentials.token

    def _set_necessary_date_headers(self, request):
        # The spec allows for either the Date _or_ the X-Amz-Date value to be
        # used so we check both.  If there's a Date header, we use the date
        # header.  Otherwise we use the X-Amz-Date header.
        if 'Date' in request.headers:
            del request.headers['Date']
            datetime_timestamp = datetime.datetime.strptime(
                request.context['timestamp'], SIGV4_TIMESTAMP)
            request.headers['Date'] = formatdate(
                int(calendar.timegm(datetime_timestamp.timetuple())))
            if 'X-Amz-Date' in request.headers:
                del request.headers['X-Amz-Date']
        else:
            if 'X-Amz-Date' in request.headers:
                del request.headers['X-Amz-Date']
            request.headers['X-Amz-Date'] = request.context['timestamp']


class S3SigV4Auth(SigV4Auth):
    def __init__(self, credentials, service_name, region_name):
        super(S3SigV4Auth, self).__init__(
            credentials, service_name, region_name)
        self._default_region_name = region_name

    def add_auth(self, request):
        # If we ever decide to share auth sessions, this could potentially be
        # a source of concurrency bugs.
        signing_context = request.context.get('signing', {})
        self._region_name = signing_context.get(
            'region', self._default_region_name)
        super(S3SigV4Auth, self).add_auth(request)

    def _modify_request_before_signing(self, request):
        super(S3SigV4Auth, self)._modify_request_before_signing(request)
        if 'X-Amz-Content-SHA256' in request.headers:
            del request.headers['X-Amz-Content-SHA256']

        if self._should_sha256_sign_payload(request):
            request.headers['X-Amz-Content-SHA256'] = self.payload(request)
        else:
            request.headers['X-Amz-Content-SHA256'] = 'UNSIGNED-PAYLOAD'

    def _should_sha256_sign_payload(self, request):
        # S3 allows optional body signing, so to minimize the performance
        # impact, we opt to not SHA256 sign the body on streaming uploads,
        # provided that we're on https.
        client_config = request.context.get('client_config')
        s3_config = getattr(client_config, 's3', None)

        # The config could be None if it isn't set, or if the customer sets it
        # to None.
        if s3_config is None:
            s3_config = {}

        sign_payload = s3_config.get('payload_signing_enabled', None)
        if sign_payload is not None:
            return sign_payload

        if 'Content-MD5' in request.headers and 'https' in request.url and \
                request.context.get('has_streaming_input', False):
            return False

        return True

    def _normalize_url_path(self, path):
        # For S3, we do not normalize the path.
        return path


class SigV4QueryAuth(SigV4Auth):
    DEFAULT_EXPIRES = 3600

    def __init__(self, credentials, service_name, region_name,
                 expires=DEFAULT_EXPIRES):
        super(SigV4QueryAuth, self).__init__(credentials, service_name,
                                             region_name)
        self._expires = expires

    def _modify_request_before_signing(self, request):
        # Note that we're not including X-Amz-Signature.
        # From the docs: "The Canonical Query String must include all the query
        # parameters from the preceding table except for X-Amz-Signature.
        signed_headers = self.signed_headers(self.headers_to_sign(request))
        auth_params = {
            'X-Amz-Algorithm': 'AWS4-HMAC-SHA256',
            'X-Amz-Credential': self.scope(request),
            'X-Amz-Date': request.context['timestamp'],
            'X-Amz-Expires': self._expires,
            'X-Amz-SignedHeaders': signed_headers,
        }
        if self.credentials.token is not None:
            auth_params['X-Amz-Security-Token'] = self.credentials.token
        # Now parse the original query string to a dict, inject our new query
        # params, and serialize back to a query string.
        url_parts = urlsplit(request.url)
        # parse_qs makes each value a list, but in our case we know we won't
        # have repeated keys so we know we have single element lists which we
        # can convert back to scalar values.
        query_dict = dict(
            [(k, v[0]) for k, v in parse_qs(url_parts.query).items()])
        # The spec is particular about this.  It *has* to be:
        # https://<endpoint>?<operation params>&<auth params>
        # You can't mix the two types of params together, i.e just keep doing
        # new_query_params.update(op_params)
        # new_query_params.update(auth_params)
        # percent_encode_sequence(new_query_params)
        operation_params = ''
        if request.data:
            # We also need to move the body params into the query string.
            # request.data will be populated, for example, with query services
            # which normally form encode the params into the body.
            # This means that request.data is a dict() of the operation params.
            query_dict.update(request.data)
            request.data = ''
        if query_dict:
            operation_params = percent_encode_sequence(query_dict) + '&'
        new_query_string = (operation_params +
                            percent_encode_sequence(auth_params))
        # url_parts is a tuple (and therefore immutable) so we need to create
        # a new url_parts with the new query string.
        # <part>   - <index>
        # scheme   - 0
        # netloc   - 1
        # path     - 2
        # query    - 3  <-- we're replacing this.
        # fragment - 4
        p = url_parts
        new_url_parts = (p[0], p[1], p[2], new_query_string, p[4])
        request.url = urlunsplit(new_url_parts)

    def _inject_signature_to_request(self, request, signature):
        # Rather than calculating an "Authorization" header, for the query
        # param quth, we just append an 'X-Amz-Signature' param to the end
        # of the query string.
        request.url += '&X-Amz-Signature=%s' % signature


class S3SigV4QueryAuth(SigV4QueryAuth):
    """S3 SigV4 auth using query parameters.

    This signer will sign a request using query parameters and signature
    version 4, i.e a "presigned url" signer.

    Based off of:

    http://docs.aws.amazon.com/AmazonS3/latest/API/sigv4-query-string-auth.html

    """
    def _normalize_url_path(self, path):
        # For S3, we do not normalize the path.
        return path

    def payload(self, request):
        # From the doc link above:
        # "You don't include a payload hash in the Canonical Request, because
        # when you create a presigned URL, you don't know anything about the
        # payload. Instead, you use a constant string "UNSIGNED-PAYLOAD".
        return "UNSIGNED-PAYLOAD"


class S3SigV4PostAuth(SigV4Auth):
    """
    Presigns a s3 post

    Implementation doc here:
    http://docs.aws.amazon.com/AmazonS3/latest/API/sigv4-UsingHTTPPOST.html
    """
    def add_auth(self, request):
        datetime_now = datetime.datetime.utcnow()
        request.context['timestamp'] = datetime_now.strftime(SIGV4_TIMESTAMP)

        fields = {}
        if request.context.get('s3-presign-post-fields', None) is not None:
            fields = request.context['s3-presign-post-fields']

        policy = {}
        conditions = []
        if request.context.get('s3-presign-post-policy', None) is not None:
            policy = request.context['s3-presign-post-policy']
            if policy.get('conditions', None) is not None:
                conditions = policy['conditions']

        policy['conditions'] = conditions

        fields['x-amz-algorithm'] = 'AWS4-HMAC-SHA256'
        fields['x-amz-credential'] = self.scope(request)
        fields['x-amz-date'] = request.context['timestamp']

        conditions.append({'x-amz-algorithm': 'AWS4-HMAC-SHA256'})
        conditions.append({'x-amz-credential': self.scope(request)})
        conditions.append({'x-amz-date': request.context['timestamp']})

        if self.credentials.token is not None:
            fields['x-amz-security-token'] = self.credentials.token
            conditions.append({'x-amz-security-token': self.credentials.token})

        # Dump the base64 encoded policy into the fields dictionary.
        fields['policy'] = base64.b64encode(
            json.dumps(policy).encode('utf-8')).decode('utf-8')

        fields['x-amz-signature'] = self.signature(fields['policy'], request)

        request.context['s3-presign-post-fields'] = fields
        request.context['s3-presign-post-policy'] = policy


class HmacV1Auth(BaseSigner):

    # List of Query String Arguments of Interest
    QSAOfInterest = ['accelerate', 'acl', 'cors', 'defaultObjectAcl',
                     'location', 'logging', 'partNumber', 'policy',
                     'requestPayment', 'torrent',
                     'versioning', 'versionId', 'versions', 'website',
                     'uploads', 'uploadId', 'response-content-type',
                     'response-content-language', 'response-expires',
                     'response-cache-control', 'response-content-disposition',
                     'response-content-encoding', 'delete', 'lifecycle',
                     'tagging', 'restore', 'storageClass', 'notification',
                     'replication', 'requestPayment']

    def __init__(self, credentials, service_name=None, region_name=None):
        self.credentials = credentials

    def sign_string(self, string_to_sign):
        new_hmac = hmac.new(self.credentials.secret_key.encode('utf-8'),
                            digestmod=sha1)
        new_hmac.update(string_to_sign.encode('utf-8'))
        return encodebytes(new_hmac.digest()).strip().decode('utf-8')

    def canonical_standard_headers(self, headers):
        interesting_headers = ['content-md5', 'content-type', 'date']
        hoi = []
        if 'Date' in headers:
            del headers['Date']
        headers['Date'] = self._get_date()
        for ih in interesting_headers:
            found = False
            for key in headers:
                lk = key.lower()
                if headers[key] is not None and lk == ih:
                    hoi.append(headers[key].strip())
                    found = True
            if not found:
                hoi.append('')
        return '\n'.join(hoi)

    def canonical_custom_headers(self, headers):
        hoi = []
        custom_headers = {}
        for key in headers:
            lk = key.lower()
            if headers[key] is not None:
                if lk.startswith('x-amz-'):
                    custom_headers[lk] = ','.join(v.strip() for v in
                                                  headers.get_all(key))
        sorted_header_keys = sorted(custom_headers.keys())
        for key in sorted_header_keys:
            hoi.append("%s:%s" % (key, custom_headers[key]))
        return '\n'.join(hoi)

    def unquote_v(self, nv):
        """
        TODO: Do we need this?
        """
        if len(nv) == 1:
            return nv
        else:
            return (nv[0], unquote(nv[1]))

    def canonical_resource(self, split, auth_path=None):
        # don't include anything after the first ? in the resource...
        # unless it is one of the QSA of interest, defined above
        # NOTE:
        # The path in the canonical resource should always be the
        # full path including the bucket name, even for virtual-hosting
        # style addressing.  The ``auth_path`` keeps track of the full
        # path for the canonical resource and would be passed in if
        # the client was using virtual-hosting style.
        if auth_path is not None:
            buf = auth_path
        else:
            buf = split.path
        if split.query:
            qsa = split.query.split('&')
            qsa = [a.split('=', 1) for a in qsa]
            qsa = [self.unquote_v(a) for a in qsa
                   if a[0] in self.QSAOfInterest]
            if len(qsa) > 0:
                qsa.sort(key=itemgetter(0))
                qsa = ['='.join(a) for a in qsa]
                buf += '?'
                buf += '&'.join(qsa)
        return buf

    def canonical_string(self, method, split, headers, expires=None,
                         auth_path=None):
        cs = method.upper() + '\n'
        cs += self.canonical_standard_headers(headers) + '\n'
        custom_headers = self.canonical_custom_headers(headers)
        if custom_headers:
            cs += custom_headers + '\n'
        cs += self.canonical_resource(split, auth_path=auth_path)
        return cs

    def get_signature(self, method, split, headers, expires=None,
                      auth_path=None):
        if self.credentials.token:
            del headers['x-amz-security-token']
            headers['x-amz-security-token'] = self.credentials.token
        string_to_sign = self.canonical_string(method,
                                               split,
                                               headers,
                                               auth_path=auth_path)
        logger.debug('StringToSign:\n%s', string_to_sign)
        return self.sign_string(string_to_sign)

    def add_auth(self, request):
        if self.credentials is None:
            raise NoCredentialsError
        logger.debug("Calculating signature using hmacv1 auth.")
        split = urlsplit(request.url)
        logger.debug('HTTP request method: %s', request.method)
        signature = self.get_signature(request.method, split,
                                       request.headers,
                                       auth_path=request.auth_path)
        self._inject_signature(request, signature)

    def _get_date(self):
        return formatdate(usegmt=True)

    def _inject_signature(self, request, signature):
        if 'Authorization' in request.headers:
            # We have to do this because request.headers is not
            # normal dictionary.  It has the (unintuitive) behavior
            # of aggregating repeated setattr calls for the same
            # key value.  For example:
            # headers['foo'] = 'a'; headers['foo'] = 'b'
            # list(headers) will print ['foo', 'foo'].
            del request.headers['Authorization']
        request.headers['Authorization'] = (
            "AWS %s:%s" % (self.credentials.access_key, signature))


class HmacV1QueryAuth(HmacV1Auth):
    """
    Generates a presigned request for s3.

    Spec from this document:

    http://docs.aws.amazon.com/AmazonS3/latest/dev/RESTAuthentication.html
    #RESTAuthenticationQueryStringAuth

    """
    DEFAULT_EXPIRES = 3600

    def __init__(self, credentials, expires=DEFAULT_EXPIRES):
        self.credentials = credentials
        self._expires = expires

    def _get_date(self):
        return str(int(time.time() + int(self._expires)))

    def _inject_signature(self, request, signature):
        query_dict = {}
        query_dict['AWSAccessKeyId'] = self.credentials.access_key
        query_dict['Signature'] = signature

        for header_key in request.headers:
            lk = header_key.lower()
            # For query string requests, Expires is used instead of the
            # Date header.
            if header_key == 'Date':
                query_dict['Expires'] = request.headers['Date']
            # We only want to include relevant headers in the query string.
            # These can be anything that starts with x-amz, is Content-MD5,
            # or is Content-Type.
            elif lk.startswith('x-amz-') or lk in ['content-md5',
                                                   'content-type']:
                query_dict[lk] = request.headers[lk]
        # Combine all of the identified headers into an encoded
        # query string
        new_query_string = percent_encode_sequence(query_dict)

        # Create a new url with the presigned url.
        p = urlsplit(request.url)
        if p[3]:
            # If there was a pre-existing query string, we should
            # add that back before injecting the new query string.
            new_query_string = '%s&%s' % (p[3], new_query_string)
        new_url_parts = (p[0], p[1], p[2], new_query_string, p[4])
        request.url = urlunsplit(new_url_parts)


class HmacV1PostAuth(HmacV1Auth):
    """
    Generates a presigned post for s3.

    Spec from this document:

    http://docs.aws.amazon.com/AmazonS3/latest/dev/UsingHTTPPOST.html
    """
    def add_auth(self, request):
        fields = {}
        if request.context.get('s3-presign-post-fields', None) is not None:
            fields = request.context['s3-presign-post-fields']

        policy = {}
        conditions = []
        if request.context.get('s3-presign-post-policy', None) is not None:
            policy = request.context['s3-presign-post-policy']
            if policy.get('conditions', None) is not None:
                conditions = policy['conditions']

        policy['conditions'] = conditions

        fields['AWSAccessKeyId'] = self.credentials.access_key

        if self.credentials.token is not None:
            fields['x-amz-security-token'] = self.credentials.token
            conditions.append({'x-amz-security-token': self.credentials.token})

        # Dump the base64 encoded policy into the fields dictionary.
        fields['policy'] = base64.b64encode(
            json.dumps(policy).encode('utf-8')).decode('utf-8')

        fields['signature'] = self.sign_string(fields['policy'])

        request.context['s3-presign-post-fields'] = fields
        request.context['s3-presign-post-policy'] = policy


# Defined at the bottom instead of the top of the module because the Auth
# classes weren't defined yet.
AUTH_TYPE_MAPS = {
    'v2': SigV2Auth,
    'v4': SigV4Auth,
    'v4-query': SigV4QueryAuth,
    'v3': SigV3Auth,
    'v3https': SigV3Auth,
    's3': HmacV1Auth,
    's3-query': HmacV1QueryAuth,
    's3-presign-post': HmacV1PostAuth,
    's3v4': S3SigV4Auth,
    's3v4-query': S3SigV4QueryAuth,
    's3v4-presign-post': S3SigV4PostAuth,

}
