要使用AWS签名v4对AWS IoT的HTTP请求进行签名，您可以按照以下步骤执行：

1. 安装所需的依赖项：AWS SDK for Python（Boto3）和Requests库。您可以使用以下命令进行安装：

pip install boto3 requests

2. 导入所需的模块：

import boto3
import requests
from requests.auth import AuthBase

3. 创建一个AWS签名v4的自定义认证类：

class AWSRequestSigner(AuthBase):
    def __init__(self, session, service):
        self._credentials = session.get_credentials()
        self._region = session.region_name or 'us-east-1'
        self._service = service

    def __call__(self, request):
        # 获取当前时间和日期
        amz_date = request.headers['X-Amz-Date']
        # 创建签名
        signature = self._get_signature(request, amz_date)
        # 添加认证头部
        request.headers['Authorization'] = signature
        return request

    def _get_signature(self, request, amz_date):
        # 获取要签名的信息
        canonical_request = self._get_canonical_request(request)
        string_to_sign = self._get_string_to_sign(amz_date, canonical_request)
        signing_key = self._get_signing_key(amz_date)

        # 使用签名密钥计算签名值
        signature = hmac.new(signing_key, string_to_sign.encode('utf-8'), hashlib.sha256).hexdigest()

        # 构建认证头部
        credential_scope = '{}/{}/{}/aws4_request'.format(amz_date[:8], self._region, self._service)
        authorization_header = 'AWS4-HMAC-SHA256 Credential={}/{}, SignedHeaders={}, Signature={}'.format(
            self._credentials.access_key, credential_scope, self._get_signed_headers(request), signature)
        return authorization_header

    def _get_canonical_request(self, request):
        # 构建规范请求字符串
        canonical_request = '{}\n{}\n{}\n{}\n{}\n{}'.format(
            request.method,
            self._get_canonical_uri(request),
            self._get_canonical_query_string(request),
            self._get_canonical_headers(request),
            self._get_signed_headers(request),
            hashlib.sha256(request.body).hexdigest())
        return canonical_request

    def _get_string_to_sign(self, amz_date, canonical_request):
        # 构建要签名的字符串
        string_to_sign = 'AWS4-HMAC-SHA256\n{}\n{}\n{}'.format(
            amz_date,
            self._get_credential_scope(amz_date),
            hashlib.sha256(canonical_request.encode('utf-8')).hexdigest())
        return string_to_sign

    def _get_signing_key(self, amz_date):
        # 计算签名密钥
        date_key = self._sign('AWS4' + self._credentials.secret_key, amz_date[:8])
        region_key = self._sign(date_key, self._region)
        service_key = self._sign(region_key, self._service)
        signing_key = self._sign(service_key, 'aws4_request')
        return signing_key

    def _sign(self, key, value):
        return hmac.new(key.encode('utf-8'), value.encode('utf-8'), hashlib.sha256).digest()

    def _get_canonical_uri(self, request):
        # 获取规范URI
        uri = request.path_url
        if uri == '/':
            return '/'
        else:
            return quote(uri, safe='')

    def _get_canonical_query_string(self, request):
        # 获取规范查询字符串
        query_params = request.url.split('?')[1:]
        query_params.sort()
        return '&'.join(query_params)

    def _get_canonical_headers(self, request):
        # 获取规范头部
        headers = {k.lower(): v.strip() for k, v in request.headers.items()}
        sorted_headers = sorted(headers.items())
        return '\n'.join(['{}:{}'.format(k, v) for k, v in sorted_headers])

    def _get_signed_headers(self, request):
        # 获取签名的头部
        headers = {k.lower() for k in request.headers.keys()}
        return ';'.join(sorted(headers))

    def _get_credential_scope(self, amz_date):
        # 获取凭证范围
        return '{}/{}/{}/aws4_request'.format(amz_date[:8], self._region, self._service)