activitypub: signing http client

Signed-off-by: Loïc Dachary <loic@dachary.org>

modules/activitypub/client.go

@@ -0,0 +1,117 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package activitypub
+
+import (
+	"bytes"
+	"crypto/rsa"
+	"crypto/x509"
+	"encoding/pem"
+	"fmt"
+	"net/http"
+
+	user_model "code.gitea.io/gitea/models/user"
+	"code.gitea.io/gitea/modules/setting"
+	"github.com/go-fed/activity/pub"
+	"github.com/go-fed/httpsig"
+)
+
+const (
+	activityStreamsContentType = "application/ld+json; profile=\"https://www.w3.org/ns/activitystreams\""
+)
+
+func containsRequiredHttpHeaders(method string, headers []string) error {
+	var hasRequestTarget, hasDate, hasDigest bool
+	for _, header := range headers {
+		hasRequestTarget = hasRequestTarget || header == httpsig.RequestTarget
+		hasDate = hasDate || header == "Date"
+		hasDigest = method == "GET" || hasDigest || header == "Digest"
+	}
+	if !hasRequestTarget {
+		return fmt.Errorf("missing http header for %s: %s", method, httpsig.RequestTarget)
+	} else if !hasDate {
+		return fmt.Errorf("missing http header for %s: Date", method)
+	} else if !hasDigest {
+		return fmt.Errorf("missing http header for %s: Digest", method)
+	}
+	return nil
+}
+
+type Client struct {
+	clock       pub.Clock
+	client      *http.Client
+	algs        []httpsig.Algorithm
+	digestAlg   httpsig.DigestAlgorithm
+	getHeaders  []string
+	postHeaders []string
+	priv        *rsa.PrivateKey
+	pubId       string
+}
+
+func NewClient(user *user_model.User, pubId string) (c *Client, err error) {
+	if err = containsRequiredHttpHeaders(http.MethodGet, setting.Federation.GetHeaders); err != nil {
+		return
+	} else if err = containsRequiredHttpHeaders(http.MethodPost, setting.Federation.PostHeaders); err != nil {
+		return
+	} else if !httpsig.IsSupportedDigestAlgorithm(setting.Federation.DigestAlgorithm) {
+		err = fmt.Errorf("unsupported digest algorithm: %s", setting.Federation.DigestAlgorithm)
+		return
+	}
+	algos := make([]httpsig.Algorithm, len(setting.Federation.Algorithms))
+	for i, algo := range setting.Federation.Algorithms {
+		algos[i] = httpsig.Algorithm(algo)
+	}
+	clock, err := NewClock()
+	if err != nil {
+		return
+	}
+
+	priv, err := GetPrivateKey(user)
+	if err != nil {
+		return
+	}
+	privPem, _ := pem.Decode([]byte(priv))
+	privParsed, err := x509.ParsePKCS1PrivateKey(privPem.Bytes)
+	if err != nil {
+		return
+	}
+
+	c = &Client{
+		clock:       clock,
+		client:      &http.Client{},
+		algs:        algos,
+		digestAlg:   httpsig.DigestAlgorithm(setting.Federation.DigestAlgorithm),
+		getHeaders:  setting.Federation.GetHeaders,
+		postHeaders: setting.Federation.PostHeaders,
+		priv:        privParsed,
+		pubId:       pubId,
+	}
+	return
+}
+
+func (c *Client) Post(b []byte, to string) (resp *http.Response, err error) {
+	byteCopy := make([]byte, len(b))
+	copy(byteCopy, b)
+	buf := bytes.NewBuffer(byteCopy)
+	var req *http.Request
+	req, err = http.NewRequest(http.MethodPost, to, buf)
+	if err != nil {
+		return
+	}
+	req.Header.Add("Content-Type", activityStreamsContentType)
+	req.Header.Add("Accept-Charset", "utf-8")
+	req.Header.Add("Date", fmt.Sprintf("%s GMT", c.clock.Now().UTC().Format("Mon, 02 Jan 2006 15:04:05")))
+
+	signer, _, err := httpsig.NewSigner(c.algs, c.digestAlg, c.postHeaders, httpsig.Signature, 60)
+	if err != nil {
+		return
+	}
+	err = signer.SignRequest(c.priv, c.pubId, req, b)
+	if err != nil {
+		return
+	}
+	resp, err = c.client.Do(req)
+	return
+}