Base64-encode U2F data sent over the public API

Create "better" JSON, rather than just dumping binary strings in it.

backend/composite_values.go

 package backend
 
 import (
+	"encoding/base64"
+
 	as "git.autistici.org/ai3/accountserver"
 	ct "git.autistici.org/ai3/go-common/ldap/compositetypes"
 )
 
+// Note: all functions below deliberately ignore deserialization
+// errors (the broken entry is just skipped). This way, broken data in
+// the database will be invisible and not break the app. Not that it
+// is an overall better strategy than crashing, but it's a bit gentler
+// on the user.
+
 func newAppSpecificPassword(info as.AppSpecificPasswordInfo, pw string) *ct.AppSpecificPassword {
 	return &ct.AppSpecificPassword{
 		ID:                info.ID,
@@ -78,10 +86,12 @@ func decodeU2FRegistrations(encRegs []string) []*as.U2FRegistration {
 	var out []*as.U2FRegistration
 	for _, enc := range encRegs {
 		if r, err := ct.UnmarshalU2FRegistration(enc); err == nil {
-			// Mirror ct.U2FRegistration -> as.U2FRegistration.
+			// Convert ct.U2FRegistration (internal) ->
+			// as.U2FRegistration (public) by
+			// base64-encoding the data.
 			out = append(out, &as.U2FRegistration{
-				KeyHandle: r.KeyHandle,
-				PublicKey: r.PublicKey,
+				KeyHandle: base64.StdEncoding.EncodeToString(r.KeyHandle),
+				PublicKey: base64.StdEncoding.EncodeToString(r.PublicKey),
 			})
 		}
 	}
@@ -91,10 +101,20 @@ func decodeU2FRegistrations(encRegs []string) []*as.U2FRegistration {
 func encodeU2FRegistrations(regs []*as.U2FRegistration) []string {
 	var out []string
 	for _, r := range regs {
-		// Mirror as.U2FRegistration -> ct.U2FRegistration.
+		// Convert as.U2FRegistration (public) ->
+		// ct.U2FRegistration (internal) by base64-decoding
+		// the data.
+		kh, err := base64.StdEncoding.DecodeString(r.KeyHandle)
+		if err != nil {
+			continue
+		}
+		pk, err := base64.StdEncoding.DecodeString(r.PublicKey)
+		if err != nil {
+			continue
+		}
 		ctr := ct.U2FRegistration{
-			KeyHandle: r.KeyHandle,
-			PublicKey: r.PublicKey,
+			KeyHandle: kh,
+			PublicKey: pk,
 		}
 		out = append(out, ctr.Marshal())
 	}

types.go

@@ -591,10 +591,10 @@ func getHostingDir(path, siteRoot string) string {
 
 // U2FRegistration stores information on a single U2F device registration.
 //
-// This is a mirror of compositetypes.U2FRegistration, but it is
-// duplicated since this is part of our public interface, and
-// compositetypes is a detail of the LDAP backend implementation.
+// This mirrors closely compositetypes.U2FRegistration, with the very
+// important difference that the data here is base64-encoded! Can't
+// reliably push arbitrary binary data through JSON otherwise.
 type U2FRegistration struct {
-	KeyHandle []byte `json:"key_handle"`
-	PublicKey []byte `json:"public_key"`
+	KeyHandle string `json:"key_handle"`
+	PublicKey string `json:"public_key"`
 }