1 files changed, 81 insertions, 0 deletions
diff --git a/tools/verifier.go b/tools/verifier.go
new file mode 100644
index 0000000..4063ccf
--- /dev/null
+++ b/tools/verifier.go
@@ -0,0 +1,81 @@
+package tools
+
+import (
+	"context"
+	"crypto/x509"
+	"encoding/json"
+	"encoding/pem"
+	"fmt"
+	"io"
+	"net/http"
+
+	"github.com/go-fed/activity/streams"
+	"github.com/go-fed/activity/streams/vocab"
+	"github.com/go-fed/httpsig"
+	"go.uber.org/zap"
+)
+
+func VerifyRequest(ctx context.Context, req *http.Request, log *zap.SugaredLogger) (vocab.ActivityStreamsPerson, error) {
+	logger := log.With("type", "verifier")
+	verifier, err := httpsig.NewVerifier(req)
+	if err != nil {
+		return nil, err
+	}
+
+	keyId := verifier.KeyId()
+	logger.With("keyId", keyId).Debugf("fetching key page")
+	req, err = http.NewRequest("GET", keyId, nil)
+	req.Header.Set("Accept", "application/json; charset=UTF-8")
+
+	client := &http.Client{}
+	resp, err := client.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+	keyPage, err := io.ReadAll(resp.Body)
+	logger.With("keyId", keyId).With("response", string(keyPage)).Debugf("received response")
+	var keyPageData map[string]interface{}
+	err = json.Unmarshal(keyPage, &keyPageData)
+	if err != nil {
+		return nil, err
+	}
+
+	var person vocab.ActivityStreamsPerson
+
+	resolver, err := streams.NewJSONResolver(func(c context.Context, p vocab.ActivityStreamsPerson) error {
+		// Store the person in the enclosing scope, for later.
+		person = p
+		return nil
+	}, func(c context.Context, note vocab.ActivityStreamsNote) error {
+		//TODO not needed, need to figure out how to only pass one func
+		return nil
+	})
+
+	err = resolver.Resolve(ctx, keyPageData)
+	if err != nil {
+		return nil, err
+	}
+
+	pubKeyProp := person.GetW3IDSecurityV1PublicKey()
+	iter := pubKeyProp.At(0) // TODO not safe, use a for instead
+	pubKey := iter.Get()
+	pemProp := pubKey.GetW3IDSecurityV1PublicKeyPem()
+	pemStr := pemProp.Get()
+	logger.With("keyId", keyId).With("pem", pemStr).Debugf("extracted pem")
+	pemObj, _ := pem.Decode([]byte(pemStr))
+	if pemObj == nil {
+		return nil, fmt.Errorf("no PEM block found")
+	}
+	if pemObj.Type != "PUBLIC KEY" {
+		return nil, fmt.Errorf("no public key found in PEM block")
+	}
+
+	decodedKey, err := x509.ParsePKIXPublicKey(pemObj.Bytes)
+	if err != nil {
+		return nil, err
+	}
+	logger.With("keyId", keyId).With("pem", pemStr).Debugf("got %T", decodedKey)
+	algo := httpsig.RSA_SHA256
+	return person, verifier.Verify(decodedKey, algo)
+}