Fix nil dereference

Forgot to initialize the wrapped u2f.Registration.

types.go

@@ -418,7 +418,7 @@ type U2FRegistration struct {
 
 // MarshalJSON implements the json.Marshaler interface.
 func (r *U2FRegistration) MarshalJSON() ([]byte, error) {
-	data, err := r.MarshalBinary()
+	data, err := r.Registration.MarshalBinary()
 	if err != nil {
 		return nil, err
 	}
@@ -434,5 +434,6 @@ func (r *U2FRegistration) UnmarshalJSON(data []byte) error {
 	if err := json.Unmarshal(data, &b); err != nil {
 		return err
 	}
-	return r.UnmarshalBinary(b)
+	r.Registration = new(u2f.Registration)
+	return r.Registration.UnmarshalBinary(b)
 }

types_test.go

+package accountserver
+
+import (
+	"encoding/json"
+	"testing"
+)
+
+var testReg = `"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"`
+
+func TestU2FRegistration_Unmarshal(t *testing.T) {
+	var reg U2FRegistration
+	if err := json.Unmarshal([]byte(testReg), &reg); err != nil {
+		t.Fatal(err)
+	}
+}