owncast/activitypub/crypto/sign.go

package crypto

import (
	"bytes"
	"crypto"
	"fmt"
	"net/http"
	"net/url"
	"time"

	"github.com/go-fed/httpsig"
	"github.com/owncast/owncast/config"
	log "github.com/sirupsen/logrus"
)

// SignResponse will sign a response using the provided response body and public key.
func SignResponse(w http.ResponseWriter, body []byte, publicKey PublicKey) error {
	privateKey := GetPrivateKey()

	return signResponse(privateKey, *publicKey.ID, body, w)
}

func signResponse(privateKey crypto.PrivateKey, pubKeyID url.URL, body []byte, w http.ResponseWriter) error {
	prefs := []httpsig.Algorithm{httpsig.RSA_SHA256}
	digestAlgorithm := httpsig.DigestSha256

	// The "Date" and "Digest" headers must already be set on r, as well as r.URL.
	headersToSign := []string{}
	if body != nil {
		headersToSign = append(headersToSign, "digest")
	}

	signer, _, err := httpsig.NewSigner(prefs, digestAlgorithm, headersToSign, httpsig.Signature, 0)
	if err != nil {
		return err
	}

	// If r were a http.ResponseWriter, call SignResponse instead.
	return signer.SignResponse(privateKey, pubKeyID.String(), w, body)
}

// SignRequest will sign an ounbound request given the provided body.
func SignRequest(req *http.Request, body []byte, actorIRI *url.URL) error {
	publicKey := GetPublicKey(actorIRI)
	privateKey := GetPrivateKey()

	return signRequest(privateKey, publicKey.ID.String(), body, req)
}

func signRequest(privateKey crypto.PrivateKey, pubKeyID string, body []byte, r *http.Request) error {
	prefs := []httpsig.Algorithm{httpsig.RSA_SHA256}
	digestAlgorithm := httpsig.DigestSha256

	date := time.Now().UTC().Format("Mon, 02 Jan 2006 15:04:05 GMT")
	r.Header["Date"] = []string{date}
	r.Header["Host"] = []string{r.URL.Host}
	r.Header["Accept"] = []string{`application/ld+json; profile="https://www.w3.org/ns/activitystreams"`}

	// The "Date" and "Digest" headers must already be set on r, as well as r.URL.
	headersToSign := []string{httpsig.RequestTarget, "host", "date"}
	if body != nil {
		headersToSign = append(headersToSign, "digest")
	}

	signer, _, err := httpsig.NewSigner(prefs, digestAlgorithm, headersToSign, httpsig.Signature, 0)
	if err != nil {
		return err
	}

	// If r were a http.ResponseWriter, call SignResponse instead.
	return signer.SignRequest(privateKey, pubKeyID, r, body)
}

// CreateSignedRequest will create a signed POST request of a payload to the provided destination.
func CreateSignedRequest(payload []byte, url *url.URL, fromActorIRI *url.URL) (*http.Request, error) {
	log.Debugln("Sending", string(payload), "to", url)

	req, _ := http.NewRequest("POST", url.String(), bytes.NewBuffer(payload))

	ua := fmt.Sprintf("%s; https://owncast.online", config.GetReleaseString())
	req.Header.Set("User-Agent", ua)
	req.Header.Set("Content-Type", "application/activity+json")

	if err := SignRequest(req, payload, fromActorIRI); err != nil {
		log.Errorln("error signing request:", err)
		return nil, err
	}

	return req, nil
}