AWS: Use instance role credentials to query ec2 API
0I was having some issues including a token in v4 signing requests using the ec2 query API. With the help of the excellent AWS support, I know have a working example based on the documentation provided by Amazon.
# AWS Version 4 signing example # EC2 API (DescribeRegions) # See: http://docs.aws.amazon.com/general/latest/gr/sigv4_signing.html # This version makes a GET request and passes the signature # in the Authorization header. import sys, os, base64, datetime, hashlib, hmac, json import requests # pip install requests # ************* REQUEST VALUES ************* method = 'GET' service = 'ec2' host = 'ec2.amazonaws.com' region = 'us-east-1' endpoint = 'https://ec2.amazonaws.com' request_parameters = 'Action=DescribeRegions&Version=2013-10-15' # Get the Role information and credentials r = requests.get('http://169.254.169.254/latest/meta-data/iam/security-credentials'); role = r.text r = requests.get('http://169.254.169.254/latest/meta-data/iam/security-credentials/' + role); decoded_data = json.loads(r.text) access_key = decoded_data['AccessKeyId'] secret_key = decoded_data['SecretAccessKey'] token = decoded_data['Token'] # 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, dateStamp, regionName, serviceName): kDate = sign(('AWS4' + key).encode('utf-8'), dateStamp) kRegion = sign(kDate, regionName) kService = sign(kRegion, serviceName) kSigning = sign(kService, 'aws4_request') return kSigning # Create a date for headers and the credential string t = datetime.datetime.utcnow() amzdate = t.strftime('%Y%m%dT%H%M%SZ') datestamp = 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 (a GET request), # request parameters are in the query string. Query string values must # be URL-encoded (space=%20). The parameters must be sorted by name. # For this example, the query string is pre-formatted in the request_parameters variable. canonical_querystring = request_parameters # Step 4: Create the canonical headers and signed headers. Header names # and value must be trimmed and lowercase, and sorted in ASCII order. # Note that there is a trailing \n. canonical_headers = 'host:' + host + '\n' + 'x-amz-date:' + amzdate + '\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 lists those that you want to be included in the # hash of the request. "Host" and "x-amz-date" are always required. signed_headers = 'host;x-amz-date' # Step 6: Create payload hash (hash of the request body content). For GET # requests, the payload is an empty string (""). payload_hash = hashlib.sha256('').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 = datestamp + '/' + region + '/' + service + '/' + 'aws4_request' string_to_sign = algorithm + '\n' + amzdate + '\n' + credential_scope + '\n' + hashlib.sha256(canonical_request).hexdigest() # ************* TASK 3: CALCULATE THE SIGNATURE ************* # Create the signing key using the function defined above. signing_key = getSignatureKey(secret_key, datestamp, 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 ************* # The signing information can be either in a query string value or in # a header named Authorization. This code shows how to use a header. # Create authorization header and add to request headers authorization_header = algorithm + ' ' + 'Credential=' + access_key + '/' + credential_scope + ', ' + 'SignedHeaders=' + signed_headers + ', ' + 'Signature=' + signature # The request can include any headers, but MUST include "host", "x-amz-date", # and (for this scenario) "Authorization". "host" and "x-amz-date" must # be included in the canonical_headers and signed_headers, as noted # earlier. Order here is not significant. # Python note: The 'host' header is added automatically by the Python 'requests' library. headers = {'x-amz-date':amzdate , 'Authorization':authorization_header, 'X-Amz-Security-Token':token} # ************* SEND THE REQUEST ************* request_url = endpoint + '?' + canonical_querystring print '\nBEGIN REQUEST++++++++++++++++++++++++++++++++++++' print 'Request URL = ' + request_url r = requests.get(request_url, headers=headers) print '\nRESPONSE++++++++++++++++++++++++++++++++++++' print 'Response code: %d\n' % r.status_code print r.text
Hopefully you find this useful.
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