1 files changed, 99 insertions, 0 deletions
diff --git a/routers/api/v1/activitypub/reqsignature.go b/routers/api/v1/activitypub/reqsignature.go
new file mode 100644
index 0000000..6003f66
--- /dev/null
+++ b/routers/api/v1/activitypub/reqsignature.go
@@ -0,0 +1,99 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package activitypub
+
+import (
+	"crypto"
+	"crypto/x509"
+	"encoding/pem"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+
+	"code.gitea.io/gitea/modules/activitypub"
+	"code.gitea.io/gitea/modules/httplib"
+	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/setting"
+	gitea_context "code.gitea.io/gitea/services/context"
+
+	ap "github.com/go-ap/activitypub"
+	"github.com/go-fed/httpsig"
+)
+
+func getPublicKeyFromResponse(b []byte, keyID *url.URL) (p crypto.PublicKey, err error) {
+	person := ap.PersonNew(ap.IRI(keyID.String()))
+	err = person.UnmarshalJSON(b)
+	if err != nil {
+		return nil, fmt.Errorf("ActivityStreams type cannot be converted to one known to have publicKey property: %w", err)
+	}
+	pubKey := person.PublicKey
+	if pubKey.ID.String() != keyID.String() {
+		return nil, fmt.Errorf("cannot find publicKey with id: %s in %s", keyID, string(b))
+	}
+	pubKeyPem := pubKey.PublicKeyPem
+	block, _ := pem.Decode([]byte(pubKeyPem))
+	if block == nil || block.Type != "PUBLIC KEY" {
+		return nil, fmt.Errorf("could not decode publicKeyPem to PUBLIC KEY pem block type")
+	}
+	p, err = x509.ParsePKIXPublicKey(block.Bytes)
+	return p, err
+}
+
+func fetch(iri *url.URL) (b []byte, err error) {
+	req := httplib.NewRequest(iri.String(), http.MethodGet)
+	req.Header("Accept", activitypub.ActivityStreamsContentType)
+	req.Header("User-Agent", "Gitea/"+setting.AppVer)
+	resp, err := req.Response()
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("url IRI fetch [%s] failed with status (%d): %s", iri, resp.StatusCode, resp.Status)
+	}
+	b, err = io.ReadAll(io.LimitReader(resp.Body, setting.Federation.MaxSize))
+	return b, err
+}
+
+func verifyHTTPSignatures(ctx *gitea_context.APIContext) (authenticated bool, err error) {
+	r := ctx.Req
+
+	// 1. Figure out what key we need to verify
+	v, err := httpsig.NewVerifier(r)
+	if err != nil {
+		return false, err
+	}
+	ID := v.KeyId()
+	idIRI, err := url.Parse(ID)
+	if err != nil {
+		return false, err
+	}
+	// 2. Fetch the public key of the other actor
+	b, err := fetch(idIRI)
+	if err != nil {
+		return false, err
+	}
+	pubKey, err := getPublicKeyFromResponse(b, idIRI)
+	if err != nil {
+		return false, err
+	}
+	// 3. Verify the other actor's key
+	algo := httpsig.Algorithm(setting.Federation.Algorithms[0])
+	authenticated = v.Verify(pubKey, algo) == nil
+	return authenticated, err
+}
+
+// ReqHTTPSignature function
+func ReqHTTPSignature() func(ctx *gitea_context.APIContext) {
+	return func(ctx *gitea_context.APIContext) {
+		if authenticated, err := verifyHTTPSignatures(ctx); err != nil {
+			log.Warn("verifyHttpSignatures failed: %v", err)
+			ctx.Error(http.StatusBadRequest, "reqSignature", "request signature verification failed")
+		} else if !authenticated {
+			ctx.Error(http.StatusForbidden, "reqSignature", "request signature verification failed")
+		}
+	}
+}