Python

Scenarios

To use Python to sign backend requests, obtain the Python SDK, import the project, and verify the backend signature by referring to the example provided in this section.

This section uses IntelliJ IDEA 2018.3.5 as an example.

Preparing the Environment

You have obtained the key and secret of the signature key to be used.
You have created a signature key on the API Gateway console and bound it to the API to be called. For more information, see "Creating and Using a Signature Key" in the User Guide.
Log in to the API Gateway console, and download the SDK on the SDKs page by referring to section "SDKs" in the User Guide.
You have installed Python 2.7 or 3.X. If not, download the Python installation package from the official Python website and install it.
You have installed IntelliJ IDEA. If not, download IntelliJ IDEA from the official IntelliJ IDEA website and install it.
You have installed the Python plug-in on IntelliJ IDEA. If not, install the Python plug-in according to Figure 1.
Figure 1 Installing the Python plug-in

Importing a Project

Start IntelliJ IDEA and choose File > New > Project.

On the displayed New Project page, choose Python and click Next.

Figure 2 New Python
Click Next. Click ..., select the directory where the SDK is decompressed, and click Finish.

Figure 3 Selecting the SDK directory of Python after decompression
View the directory structure shown in the following figure.

Figure 4 Directory structure
Click Edit Configurations.

Figure 5 Edit Configurations
Click + and choose Flask server.

Figure 6 Choosing Flask server
Set Target type to Script path, select backend_signature.py from the Target drop-down list box, and click OK.

Backend Signature Verification Example

This example demonstrates how to build a Flask-based server as the backend of an API and implement a wrapper to verify the signature of requests sent from API Gateway (API Management).

Signature information is added to requests sent to access the backend of an API only after a signature key is bound to the API.

Compile an interface that returns Hello World! Configure the GET, POST, PUT, and DELETE methods and the requires_apigateway_signature wrapper.

app = Flask(__name__)

@app.route("/<id>", methods=['GET', 'POST', 'PUT', 'DELETE'])
@requires_apigateway_signature()
def hello(id):
    return "Hello World!"

Implement requires_apigateway_signature by putting the signature key and secret in a dict.

def requires_apigateway_signature():
    def wrapper(f):

        secrets = {
            "signature_key1": "signature_secret1",
            "signature_key2": "signature_secret2",
        }
        authorizationPattern = re.compile(
            r'SDK-HMAC-SHA256\s+Access=([^,]+),\s?SignedHeaders=([^,]+),\s?Signature=(\w+)')
        BasicDateFormat = "%Y%m%dT%H%M%SZ"

        @wraps(f)
        def wrapped(*args, **kwargs):
            //Signature verification code
            ...

            return f(*args, **kwargs)
        return wrapped
    return wrapper

Use a regular expression to parse the Authorization header. The key and signedHeaders are obtained. The wrapped function is used for signature verification.

if "authorization" not in request.headers:
	return 'Authorization not found.', 401
authorization = request.headers['authorization']
m = authorizationPattern.match(authorization)
if m is None:
	return 'Authorization format incorrect.', 401
signingKey = m.group(1)
signedHeaders = m.group(2).split(";")

For example, for Authorization header:

1	SDK-HMAC-SHA256 Access=signature_key1, SignedHeaders=host;x-sdk-date, Signature=e11adf65a20d1b82c25419b5********8d0ba12fed1ceb13ed00

The parsing result is as follows:

1 2	signingKey=signature_key1 signedHeaders=host;x-sdk-date

Find secret based on key. If key does not exist, the authentication failed.

1
2
3

if signingKey not in secrets:
	return 'Signing key not found.', 401
signingSecret = secrets[signingKey]

Create an HttpRequest, and add the method, URL, query, and signedHeaders headers to the request. Determine whether the body needs to be set.

The body is read if there is no x-sdk-content-sha256 header with value UNSIGNED-PAYLOAD.

r = signer.HttpRequest()
r.method = request.method
r.uri = request.path
r.query = {}
for k in request.query_string.decode('utf-8').split('&'):
	spl = k.split("=", 1)
	if len(spl) < 2:
		r.query[spl[0]] = ""
	else:
		r.query[spl[0]] = spl[1]
r.headers = {}
needbody = True
dateHeader = None
for k in signedHeaders:
	if k not in request.headers:
		return 'Signed header ' + k + ' not found', 401
	v = request.headers[k]
	if k.lower() == 'x-sdk-content-sha256' and v == 'UNSIGNED-PAYLOAD':
		needbody = False
	if k.lower() == 'x-sdk-date':
		dateHeader = v
	r.headers[k] = v
if needbody:
	r.body = request.get_data()

Check whether the signature has expired. Obtain the time from the X-Sdk-Date header, and check whether the difference between this time and the server time is within 15 minutes. If signedHeaders does not contain X-Sdk-Date, the authentication failed.

if dateHeader is None:
	return 'Header x-sdk-date not found.', 401
t = datetime.strptime(dateHeader, BasicDateFormat)
if abs(t - datetime.utcnow()) > timedelta(minutes=15):
	return 'Signature expired.', 401

Invoke the verify method to verify the signature of the request, and check whether the verification is successful.

sig = signer.Signer()
sig.Key = signingKey
sig.Secret = signingSecret
if not sig.Verify(r, m.group(3)):
	return 'Verify authroization failed.', 401

Run the server to verify the code. The following example uses the HTML signature tool in the JavaScript SDK to generate a signature.

Set the parameters according to the following figure, and click Send request. Copy the generated curl command, execute it in the CLI, and check whether the server returns 200.

If an incorrect key or secret is used, the server returns 401, which means authentication failure.