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#include <mod/jwt.hxx>
#include <libbutl/base64.hxx>
#include <libbutl/openssl.hxx>
#include <libbutl/timestamp.hxx>
#include <libbutl/json/serializer.hxx>
using namespace std;
using namespace butl;
// Note that only GitHub's requirements are implemented, not the entire JWT
// spec. The following elements are currently supported:
//
// - The RS256 message authentication code algorithm (RSA with SHA256)
// - The `typ` and `alg` header fields
// - The `iat`, `exp`, and `iss` claims
//
// A JWT consists of a message and its signature.
//
// The message consists of a base64url-encoded JSON header and payload (set of
// claims). The signature is calculated over the message and then also
// base64url-encoded.
//
// base64url is base64 with a slightly different alphabet and optional padding
// to make it URL and filesystem safe. See base64.hxx for details.
//
// Header:
//
// {
// "typ": "JWT",
// "alg": "RS256"
// }
//
// Payload:
//
// {
// "iat": 1234567,
// "exp": 1234577,
// "iss": "MyName"
// }
//
// Where:
// iat := Issued At (NumericDate: seconds since 1970-01-01T00:00:00Z UTC)
// exp := Expiration Time (NumericDate)
// iss := Issuer
//
// Signature:
//
// RSA_SHA256(PKEY, base64url($header) + '.' + base64url($payload))
//
// JWT:
//
// base64url($header) + '.' + base64url($payload) + '.' + base64url($signature)
//
string
brep::gen_jwt (const options::openssl_options& o,
const path& pk,
const string& iss,
const std::chrono::minutes& vp)
{
// Create the header.
//
string h; // Header (base64url-encoded).
{
vector<char> b;
json::buffer_serializer s (b);
s.begin_object ();
s.member ("typ", "JWT");
s.member ("alg", "RS256"); // RSA with SHA256.
s.end_object ();
h = base64url_encode (b);
}
// Create the payload.
//
string p; // Payload (base64url-encoded).
{
using namespace std::chrono;
// "Issued at" time.
//
// @@ TODO GitHub recommends setting this time to 60 seconds in the past
// to combat clock drift. Seems likely to be a general problem
// with client/server authentication schemes so perhaps passing
// the expected drift/skew as an argument might make sense?
//
seconds iat (
duration_cast<seconds> (system_clock::now ().time_since_epoch ()));
// Expiration time.
//
seconds exp (iat + vp);
vector<char> b;
json::buffer_serializer s (b);
s.begin_object ();
s.member ("iss", iss);
s.member ("iat", iat.count ());
s.member ("exp", exp.count ());
s.end_object ();
p = base64url_encode (b);
}
// Create the signature.
//
// The signature (base64url-encoded). Will be left empty if openssl exits
// with a non-zero status.
//
string s;
{
// Sign the concatenated header and payload using openssl.
//
// openssl dgst -sha256 -sign <pkey> file...
//
// Note that RSA is indicated by the contents of the private key.
//
openssl os (path ("-"), // Read message from openssl::out.
path ("-"), // Write output to openssl::in.
2, // Diagnostics to stderr.
process_env (o.openssl (), o.openssl_envvar ()),
"dgst", o.openssl_option (), "-sha256", "-sign", pk);
// Write the concatenated header and payload to openssl's input.
//
os.out << h << '.' << p;
os.out.close ();
// Read the binary signature from openssl's output.
//
vector<char> bs (os.in.read_binary ());
os.in.close ();
if (os.wait ())
s = base64url_encode (bs);
}
// Return the token, or empty if openssl exited with a non-zero status.
//
return !s.empty ()
? h + '.' + p + '.' + s
: "";
}
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