Rust Requires Chilkat v11.0.0+

Verify Signature of Alexa Custom Skill Request

See more HTTP Misc Examples

This example verifies the signature of an Alexa Custom Skill Request. Rust

// This example assumes you have a web service that will receive requests from Alexa.
// A sample request sent by Alexa will look like the following:

// Connection: Keep-Alive
// Content-Length: 2583
// Content-Type: application/json; charset=utf-8
// Accept: application/json
// Accept-Charset: utf-8
// Host: your.web.server.com
// User-Agent: Apache-HttpClient/4.5.x (Java/1.8.0_172)
// Signature: dSUmPwxc9...aKAf8mpEXg==
// SignatureCertChainUrl: https://s3.amazonaws.com/echo.api/echo-api-cert-6-ats.pem
// 
// {"version":"1.0","session":{"new":true,"sessionId":"amzn1.echo-api.session.433 ... }}

// First, assume we've written code to get the 3 pieces of data we need:
let signature = "dSUmPwxc9...aKAf8mpEXg==".to_string();
let cert_chain_url = "https://s3.amazonaws.com/echo.api/echo-api-cert-6-ats.pem".to_string();
let json_body = "{\"version\":\"1.0\",\"session\":{\"new\":true,\"sessionId\":\"amzn1.echo-api.session.433 ... }}".to_string();

// To validate the signature, we do the following:

// First, download the PEM-encoded X.509 certificate chain that Alexa used to sign the message 
let http = chilkat::Http::new();
let sb_pem = chilkat::StringBuilder::new();
if http.quick_get_sb(&cert_chain_url, &sb_pem).is_err() {
    println!("{}", http.last_error_text());
    return;
}

let pem = chilkat::Pem::new();
if pem.load_pem(&sb_pem.get_as_string().unwrap_or_default(), "passwordNotUsed").is_err() {
    println!("{}", pem.last_error_text());
    return;
}

// The 1st certificate should be the signing certificate.
let Ok(cert) = pem.get_cert(0) else {
    println!("{}", pem.last_error_text());
    return;
};

// Get the public key from the cert.
let pub_key = chilkat::PublicKey::new();
let _ = cert.get_public_key(&pub_key);

// Use the public key extracted from the signing certificate to decrypt the encrypted signature to produce the asserted hash value.
let rsa = chilkat::Rsa::new();
if rsa.use_public_key(&pub_key).is_err() {
    println!("{}", cert.last_error_text());
    return;
}

// RSA "decrypt" the signature.
// (Amazon's documentation is confusing, because we're simply verifiying the signature against the SHA-1 hash
// of the request body.  This happens in a single call to VerifyStringENC...)
rsa.set_encoding_mode("base64");
if rsa.verify_string_enc(&json_body, "sha1", &signature).is_ok() {
    println!("The signature is verified against the JSON body of the request. Yay!");
} else {
    println!("Sorry, not verified.  Crud!");
}