2 files changed, 150 insertions, 0 deletions
diff --git a/pkg/stryder/stryder.go b/pkg/stryder/stryder.go
index 20d5b66..35bffbb 100644
--- a/pkg/stryder/stryder.go
+++ b/pkg/stryder/stryder.go
@@ -1,3 +1,111 @@
 // Package stryder is a client for parts of the Stryder API used by Northstar
 // for authentication and license verification.
 package stryder
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strconv"
+	"strings"
+)
+
+var (
+	ErrStryder               = errors.New("internal stryder error")
+	ErrInvalidToken          = errors.New("invalid token")
+	ErrMultiplayerNotAllowed = errors.New("multiplayer not allowed")
+	ErrInvalidGame           = errors.New("invalid game")
+)
+
+// NucleusAuth verifies the provided scoped nucleus token and uid for Titanfall
+// 2 multiplayer.
+func NucleusAuth(ctx context.Context, token string, uid uint64) ([]byte, error) {
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, "https://r2-pc.stryder.respawn.com/nucleus-oauth.php?qt=origin-requesttoken&type=server_token&code="+url.PathEscape(token)+"&forceTrial=0&proto=0&json=1&&env=production&userId="+strings.ToUpper(strconv.FormatUint(uid, 16)), nil)
+	if err != nil {
+		return nil, err
+	}
+
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+
+	return nucleusAuth(resp)
+}
+
+func nucleusAuth(r *http.Response) ([]byte, error) {
+	buf, err := io.ReadAll(r.Body)
+	if err != nil {
+		return nil, err
+	}
+
+	// clean it up a bit
+	buf = bytes.TrimSpace(buf)
+
+	// check if the response is empty
+	if len(buf) == 0 {
+		return buf, fmt.Errorf("%w: empty response", ErrStryder)
+	}
+
+	// the subset of the response that we care about
+	var obj struct {
+		// error
+		Success *bool       `json:"success,omitempty"`
+		Status  json.Number `json:"status,omitempty"`
+		Error   any         `json:"error,omitempty"`
+
+		// success
+		StoreURI        string      `json:"storeUri,omitempty"`
+		HasOnlineAccess json.Number `json:"hasOnlineAccess,omitempty"`
+	}
+
+	// parse it as normal json
+	if err = json.Unmarshal(buf, &obj); err != nil {
+		// fix nested json objects inserted as-is
+		tmp := bytes.ReplaceAll(buf, []byte(`"{`), []byte(`{`))
+		tmp = bytes.ReplaceAll(tmp, []byte(`}"`), []byte(`}`))
+
+		// parse the fixed json, but return the original error if it's also bad
+		if json.Unmarshal(tmp, &obj) != nil {
+			return buf, fmt.Errorf("%w: invalid json response %#q: %v", ErrStryder, string(buf), err)
+		}
+	}
+
+	// check if it's a stryder error response
+	if obj.Success != nil && !*obj.Success {
+		// check if the error is an origin one (i.e., a nested json object) and if it's for an invalid/expired token
+		if castOr(castOr(obj.Error, map[string]any{})["error"], "") == "invalid_grant" {
+			return buf, ErrInvalidToken
+		}
+
+		// some other error
+		oerr, _ := json.Marshal(obj.Error)
+		return buf, fmt.Errorf("%w: error response %#q (status %#v)", ErrStryder, oerr, obj.Status)
+	}
+
+	// ensure the token is for the correct game
+	if !strings.Contains(obj.StoreURI, "/titanfall-2") {
+		return buf, ErrInvalidGame
+	}
+
+	// ensure hasOnlineAccess is true
+	if obj.HasOnlineAccess != "1" {
+		return buf, ErrMultiplayerNotAllowed
+	}
+
+	// otherwise it's fine
+	return buf, nil
+}
+
+func castOr[T any](v any, d T) T {
+	if x, ok := v.(T); ok {
+		return x
+	}
+	return d
+}
diff --git a/pkg/stryder/stryder_test.go b/pkg/stryder/stryder_test.go
new file mode 100644
index 0000000..23ce717
--- /dev/null
+++ b/pkg/stryder/stryder_test.go
@@ -0,0 +1,42 @@
+package stryder
+
+import (
+	"bytes"
+	"errors"
+	"io"
+	"net/http"
+	"strings"
+	"testing"
+)
+
+func TestNucleusAuth(t *testing.T) {
+	testNucleusAuth(t, "Success", `{"token":"...","hasOnlineAccess":"1","expiry":"14399","storeUri":"https://www.origin.com/store/titanfall/titanfall-2/standard-edition"}`, nil)
+	testNucleusAuth(t, "NoMultiplayer", `{"token":"...","hasOnlineAccess":"0","expiry":"14399","storeUri":"https://www.origin.com/store/titanfall/titanfall-2/standard-edition"}`, ErrMultiplayerNotAllowed)
+	testNucleusAuth(t, "InvalidToken", `{"success": false, "status": "400", "error": "{"error":"invalid_grant","error_description":"code is invalid","code":100100}"}`, ErrInvalidToken)
+	testNucleusAuth(t, "StryderBadRequest", `{"success": false, "status": "400", "error": "{"error":"invalid_request","error_description":"code is not issued to this environment","code":100119}"}`, ErrStryder)
+	testNucleusAuth(t, "StryderBadEndpoint", ``, ErrStryder)
+	testNucleusAuth(t, "StryderGoAway", "Go away.\n", ErrStryder)
+	testNucleusAuth(t, "InvalidGame", `{"token":"...","hasOnlineAccess":"1","expiry":"1234","storeUri":"https://www.origin.com/store/titanfall/titanfall-3/future-edition"}`, ErrInvalidGame) // never seen this, but test it
+}
+
+func testNucleusAuth(t *testing.T, name, resp string, res error) {
+	t.Run(name, func(t *testing.T) {
+		buf, err := nucleusAuth(&http.Response{
+			Status:     "200 OK",
+			StatusCode: 200,
+			Body:       io.NopCloser(strings.NewReader(resp)),
+		})
+		if !bytes.Equal(buf, bytes.TrimSpace([]byte(resp))) {
+			t.Errorf("returned response %q doesn't match original response %q", string(buf), string(resp))
+		}
+		if res == nil {
+			if err != nil {
+				t.Errorf("unexpected error (resp %q): %v", resp, err)
+			}
+		} else {
+			if !errors.Is(err, res) {
+				t.Errorf("expected error %q, got %q", res, err)
+			}
+		}
+	})
+}