chrome.certificateProvider

Usage

Typical usage of this API to expose client certificates to Chrome OS follows these steps:

• The Extension registers for the events onCertificatesRequested and onSignDigestRequested.
• During a TLS handshake, the browser receives a client certificate request. With a onCertificatesRequested event, the browser asks the Extension to report all certificates that it currently provides.
• The Extension reports back with the currently available certificates, using the callback that was provided with the event.
• The browser matches all available certificates with the client certificate request from the remote host. The matches are presented to the user in a selection dialog.
• The user can select a certificate and thereby approve the authentication or abort the authentication.

  

• If the user aborts the authentication or no certificate matched the request, the TLS client authentication is aborted.
• Otherwise, if the user approves the authentication with a certificate provided by this Extension, the browser requests the Extension to sign a digest to continue the TLS handshake. The request is sent as a onSignDigestRequested event.
• This event contains a digest, declares which hash function was used to create the digest, and refers to one of the certificates that were reported by this Extension in reaction to the most recent certificate request. The Extension must create a signature for the given digest using the private key associated with the referenced certificate. Creating the signature might require prepending a DigestInfo and padding the result before the actual signing.
• The Extension sends back the signature to the browser using the callback that was provided as part of the event. If the signature couldn't be calculated, the callback is called without signature.
• If the signature was provided, the browser completes the TLS handshake.

The actual sequence of steps can be different. For example, the user will not be asked to select a certificate if the enterprise policy to automatically select a certificate is used (see AutoSelectCertificateForUrls and Chrome policies for users).

In the Extension, this can look similar to the following snippet:

      function onCertificatesRejected(rejectedCerts) {
        // If certificates were rejected by the API, log an error, for example.
        console.error(rejectedCerts.length + ' certificates were rejected.');
      }
      
      function reportCertificates(reportCallback) {
        var certs = [];
        // Fill |certs| with all certificates that this Extension provides.
        // For example:
        var certInfo = {
          certificate: new Uint8Array(...),
          supportedHashes: ['SHA256']
        };
        certs.push(certInfo);
      
        reportCallback(certs, function(rejectedCerts) {
          if (chrome.runtime.lastError) {
            // Handle API errors, like argument type errors.
            return;
          }
          if (rejectedCerts.length !== 0)
            onCertificatesRejected(rejectedCerts);
        });
      }
      
      // Returns a private key handle for the given DER-encoded certificate.
      // |certificate| is an ArrayBuffer.
      function getPrivateKeyHandle(certificate) {...}
      
      // If required, prepends |digest| with a DigestInfo and pads the result
      // according to the key type and the given Hash function.
      // |digest| is an ArrayBuffer. |hash| is a Hash. Returns an ArrayBuffer.
      function prepareDigest(digest, hash) {...}
      
      // Signs |digest| with the given private key. |digest| is an ArrayBuffer.
      // Returns the signature as ArrayBuffer.
      function signDigest(privateKey, digest) {...}
      
      function reportSignature(signRequest, reportCallback) {
        // Look up the handle to the private key of |signRequest.certificate|.
        var key = getPrivateKeyHandle(signRequest.certificate);
        if (!key) {
          // Handle if the key isn't available.
          console.error('Key for requested certificate no available.');
      
          // Abort the request by reporting the error to the API.
          reportCallback();
          return;
        }
      
        var preparedDigest = prepareDigest(signRequest.digest, signRequest.hash);
        var signature = signDigest(key, preparedDigest);
      
        reportCallback(signature);
      }
      
      chrome.certificateProvider.onCertificatesRequested.addListener(
          reportCertificates);
      chrome.certificateProvider.onSignDigestRequested.addListener(
          reportSignature);
      

Summary