title: AWS SigV4 request signature does not match
body: <p>I am getting Invalid Request with below error message when trying to create a thing-type using Rest API. I am not using aws-sdk rather python rest client. </p>
  
  <p>I followed the <a href="http://docs.aws.amazon.com/general/latest/gr/sigv4-signed-request-examples.html" rel="nofollow noreferrer">steps given here</a> to sign the request using sigv4. The example given there is working for listing the Thing-Types. So the credentials I am using, are correct. Error Message :</p>
  
  <blockquote>
    <p><em>Response code: 403</em></p>
    
    <p><em>{"message":"The request signature we calculated does not match the signature you provided. Check your AWS Secret Access Key and signing
    method. Consult the service documentation for details."}</em></p>
  </blockquote>
  
  <p>The code I am using :</p>
  
  <pre><code># See: http://docs.aws.amazon.com/general/latest/gr/sigv4_signing.html
  # This version makes a POST request and passes request parameters
  # in the body (payload) of the request. Auth information is passed in
  # an Authorization header.
  import sys, os, base64, datetime, hashlib, hmac
  import requests  # pip install requests
  
  # ************* REQUEST VALUES *************
  method = 'POST'
  service = 'execute-api'
  api = 'https://iot.eu-west-2.amazonaws.com/thing-types/GasSensor'
  request_parameter='{"thingTypeProperties":{"searchableAttributes":  ["gas"],"thingTypeDescription":"Devices that reports gas level readings"}}'
  host = api.split('/')[2] if api.count('/') &gt;= 2 else ''
  region = api.split('.')[1] if api.count('.') &gt;= 1 else ''
  endpoint = api.split('?')[0] if api.count('?') &gt;= 0 else api
  #request_parameters = api.split('?')[1] if api.__contains__('?') else ''
  
  
  # Request parameters for CreateTable--passed in a JSON block.
  request_parameters = payload
  print(host + ' $ ' + region + ' $ ' + endpoint + ' $ ' + request_parameters)
  # Key derivation functions. See:
  # http://docs.aws.amazon.com/general/latest/gr/signature-v4-examples.html#signature-v4-examples-python
  def sign(key, msg):
      return hmac.new(key, msg.encode("utf-8"), hashlib.sha256).digest()
  
  def getSignatureKey(key, date_stamp, regionName, serviceName):
      kDate = sign(('AWS4' + key).encode('utf-8'), date_stamp)
      kRegion = sign(kDate, regionName)
      kService = sign(kRegion, serviceName)
      kSigning = sign(kService, 'aws4_request')
      return kSigning
  
  # Read AWS access key from env. variables or configuration file. Best practice is NOT
  # to embed credentials in code.
  access_key = 'XXXXXXXXXXXXX'
  secret_key = 'XXXXXXXXXXXXXX'   
  if access_key is None or secret_key is None:
      print
      'No access key is available.'
      sys.exit()
  
  # Create a date for headers and the credential string
  t = datetime.datetime.utcnow()
  amz_date = t.strftime('%Y%m%dT%H%M%SZ')
  date_stamp = t.strftime('%Y%m%d')  # Date w/o time, used in credential scope
  
  # ************* TASK 1: CREATE A CANONICAL REQUEST *************
  # http://docs.aws.amazon.com/general/latest/gr/sigv4-create-canonical-request.html
  
  # Step 1 is to define the verb (GET, POST, etc.)--already done.
  
  # Step 2: Create canonical URI--the part of the URI from domain to query
  # string (use '/' if no path)
  canonical_uri = '/'
  
  ## Step 3: Create the canonical query string. In this example, request
  # parameters are passed in the body of the request and the query string
  # is blank.
  canonical_querystring = ''
  
  # Step 4: Create the canonical headers. Header names must be trimmed
  # and lowercase, and sorted in code point order from low to high.
  # Note that there is a trailing \n.
  canonical_headers = 'content-type:' + content_type + '\n' + 'host:' + host + '\n' + 'x-amz-date:' + amz_date + '\n'
  
  # Step 5: Create the list of signed headers. This lists the headers
  # in the canonical_headers list, delimited with ";" and in alpha order.
  # Note: The request can include any headers; canonical_headers and
  # signed_headers include those that you want to be included in the
  # hash of the request. "Host" and "x-amz-date" are always required.
  # For DynamoDB, content-type and x-amz-target are also required.
  signed_headers = 'content-type;host;x-amz-date'
  
  # Step 6: Create payload hash. In this example, the payload (body of
  # the request) contains the request parameters.
  payload_hash = hashlib.sha256(request_parameters.encode('utf-8')).hexdigest()
  
  # Step 7: Combine elements to create create canonical request
  canonical_request = method + '\n' + canonical_uri + '\n' + canonical_querystring + '\n' + canonical_headers + '\n' + signed_headers + '\n' + payload_hash
  
  # ************* TASK 2: CREATE THE STRING TO SIGN*************
  # Match the algorithm to the hashing algorithm you use, either SHA-1 or
  # SHA-256 (recommended)
  algorithm = 'AWS4-HMAC-SHA256'
  credential_scope = date_stamp + '/' + region + '/' + service + '/' + 'aws4_request'
  string_to_sign = algorithm + '\n' + amz_date + '\n' + credential_scope + '\n' + hashlib.sha256(
      canonical_request.encode('utf-8')).hexdigest()
  
  # ************* TASK 3: CALCULATE THE SIGNATURE *************
  # Create the signing key using the function defined above.
  signing_key = getSignatureKey(secret_key, date_stamp, region, service)
  
  # Sign the string_to_sign using the signing_key
  signature = hmac.new(signing_key, (string_to_sign).encode('utf-8'), hashlib.sha256).hexdigest()
  
  # ************* TASK 4: ADD SIGNING INFORMATION TO THE REQUEST *************
  # Put the signature information in a header named Authorization.
  authorization_header = algorithm + ' ' + 'Credential=' + access_key + '/' + credential_scope + ', ' + 'SignedHeaders=' + signed_headers + ', ' + 'Signature=' + signature
  
  # # Python note: The 'host' header is added automatically by the Python 'requests' library.
  headers = {'Content-Type': content_type,
             'X-Amz-Date': amz_date,
             'Authorization': authorization_header}
  
  # ************* SEND THE REQUEST *************
  print('\nBEGIN REQUEST++++++++++++++++++++++++++++++++++++')
  
  print( 'Request URL = ' + endpoint)
  
  
  r = requests.post(endpoint, data=request_parameters, headers=headers)
  
  print('\nRESPONSE++++++++++++++++++++++++++++++++++++')
  print('Response code: %d\n' % r.status_code)
  print(r.text)
  </code></pre>