使用 python 在 s3 存储桶上获取问题

Question

我正在尝试使用来自 amazon docs 的 python 示例代码在 s3 存储桶上执行“带有授权标头的 GET”机制。我正在使用的源代码如下：

# 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
import requests # pip install requests

# ************* REQUEST VALUES *************
method = 'GET'
service = 's3'
host = 's3.amazonaws.com'
region = 'us-east-1'
endpoint = 'http://s3.amazonaws.com/sample_object/foo'
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, 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

# Read AWS access key from env. variables or configuration file. Best practice is NOT
# to embed credentials in code.
access_key = os.environ.get('AWS_ACCESS_KEY_ID')
secret_key = os.environ.get('AWS_SECRET_ACCESS_KEY')
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()
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 = '/sample_object/foo'

# 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.
# amz_content_sha256 = hashlib.sha256('').hexdigest()
amz_content_sha256 = 'UNSIGNED-PAYLOAD'
canonical_headers = 'host:' + host + '\n' + 'x-amz-content-sha256:' + amz_content_sha256 + '\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-content-sha256;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_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-content-sha256':amz_content_sha256}


# ************* SEND THE REQUEST *************
request_url = endpoint

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

我已正确设置访问 ID 和秘密访问密钥。我对 boto python 库使用了相同的方法，当我列出存储桶、放置对象等时，它似乎可以工作。但是，当我使用上述方法时，我得到一个 403 错误，说“我们计算的请求签名与您提供的签名不匹配。检查您的密钥和签名方法。”我不确定上述方法有什么问题。任何指针。？

Answer 1

规范标题应该有一个尾随换行符，canonical_request 需要 canonical_querystring 行，即使它是空白的。另外，对于 GET 请求，使用 UNSIGNED_PAYLOAD 表示 amz_content_sha256。

这是一个工作示例。它在名为bucket 的us-west-2 区域的S3 存储桶上获取一个名为key 的文件：

import sys, os, base64, datetime, hashlib, hmac
import requests
method = 'GET'
service = 's3'
host = 's3-us-west-2.amazonaws.com'
region = 'us-west-2'
endpoint = 'http://s3-us-west-2.amazonaws.com'
request_parameters = ''

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

access_key = os.environ.get('AWS_ACCESS_KEY_ID')
secret_key = os.environ.get('AWS_SECRET_ACCESS_KEY')
if access_key is None or secret_key is None:
    print 'No access key is available.'
    sys.exit()

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

canonical_uri = '/bucket/key'
canonical_querystring = request_parameters
canonical_headers = 'host:' + host + '\n' + 'x-amz-content-sha256:UNSIGNED-PAYLOAD' + '\n' + 'x-amz-date:' + amzdate + '\n'
signed_headers = 'host;x-amz-content-sha256;x-amz-date'
payload_hash = 'UNSIGNED-PAYLOAD'
canonical_request = method + '\n' + canonical_uri + '\n' + canonical_querystring + '\n' + canonical_headers + '\n' + signed_headers + '\n' + payload_hash
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()
signing_key = getSignatureKey(secret_key, datestamp, region, service)
signature = hmac.new(signing_key, (string_to_sign).encode('utf-8'), hashlib.sha256).hexdigest()
authorization_header = algorithm + ' ' + 'Credential=' + access_key + '/' + credential_scope + ', ' +  'SignedHeaders=' + signed_headers + ', ' + 'Signature=' + signature
headers = {'x-amz-date':amzdate, 'x-amz-content-sha256': 'UNSIGNED-PAYLOAD', 'Authorization':authorization_header}
request_url = endpoint + canonical_uri

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