fix: facebook auth

pkg/oauth/oauth.go

@@ -17,7 +17,9 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"log"
 	"net/http"
+	"net/url"
 	"strings"
 
 	"golang.org/x/oauth2"
@@ -150,6 +152,11 @@ type facebook struct{ id, secret string }
 
 func (f *facebook) Name() string { return "facebook" }
 
+// Bump in lockstep with whatever version your Meta app is configured for
+// (Settings → Basic → API Version). Stay on a single supported version so
+// /me responses match the documented schema.
+const facebookGraphVersion = "v25.0"
+
 func (f *facebook) Config(redirectURL string) *oauth2.Config {
 	return &oauth2.Config{
 		ClientID:     f.id,
@@ -157,8 +164,8 @@ func (f *facebook) Config(redirectURL string) *oauth2.Config {
 		RedirectURL:  redirectURL,
 		Scopes:       []string{"email", "public_profile"},
 		Endpoint: oauth2.Endpoint{
-			AuthURL:  "https://www.facebook.com/v18.0/dialog/oauth",
-			TokenURL: "https://graph.facebook.com/v18.0/oauth/access_token",
+			AuthURL:  "https://www.facebook.com/" + facebookGraphVersion + "/dialog/oauth",
+			TokenURL: "https://graph.facebook.com/" + facebookGraphVersion + "/oauth/access_token",
 		},
 	}
 }
@@ -187,8 +194,18 @@ type facebookMe struct {
 }
 
 func (f *facebook) FetchProfile(ctx context.Context, tok *oauth2.Token) (*Profile, error) {
-	const url = "https://graph.facebook.com/v18.0/me?fields=id,email,name,picture.type(large)"
-	body, err := httpGet(ctx, tok, url)
+	// Facebook Graph API: pass the token as ?access_token=... (their
+	// canonical mode) rather than via Bearer header. Bearer works most
+	// of the time but is documented as a secondary mode and has been
+	// reported to silently drop fields in some Graph versions.
+	params := url.Values{
+		"fields":       {"id,email,name,picture.type(large)"},
+		"access_token": {tok.AccessToken},
+	}
+	reqURL := "https://graph.facebook.com/" + facebookGraphVersion +
+		"/me?" + params.Encode()
+
+	body, err := plainGet(ctx, reqURL)
 	if err != nil {
 		return nil, fmt.Errorf("facebook /me: %w", err)
 	}
@@ -199,6 +216,12 @@ func (f *facebook) FetchProfile(ctx context.Context, tok *oauth2.Token) (*Profil
 	if u.ID == "" {
 		return nil, fmt.Errorf("facebook /me: empty id")
 	}
+	// If email permission was granted but FB still didn't return one,
+	// log the raw response so the operator can diagnose (commonly the
+	// user's FB account email is unverified — Graph API omits it silently).
+	if u.Email == "" {
+		log.Printf("oauth/facebook: /me returned no email; raw=%s", truncate(body, 512))
+	}
 	return &Profile{
 		Provider:       "facebook",
 		ProviderUserID: u.ID,
@@ -209,9 +232,35 @@ func (f *facebook) FetchProfile(ctx context.Context, tok *oauth2.Token) (*Profil
 	}, nil
 }
 
-// httpGet performs a token-authenticated GET and returns the response body.
-// The provider tokens include their auth header already (Bearer for Google,
-// query-param for Facebook), so we let oauth2.Client handle it.
+func truncate(b []byte, n int) string {
+	if len(b) <= n {
+		return string(b)
+	}
+	return string(b[:n]) + "…"
+}
+
+// plainGet performs an unauthenticated GET (the caller is expected to have
+// already embedded any access token in the URL). Used by Facebook because
+// Graph API treats `?access_token=` as the canonical auth mode.
+func plainGet(ctx context.Context, url string) ([]byte, error) {
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
+	if err != nil {
+		return nil, err
+	}
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		body, _ := io.ReadAll(resp.Body)
+		return nil, fmt.Errorf("status %d: %s", resp.StatusCode, string(body))
+	}
+	return io.ReadAll(resp.Body)
+}
+
+// httpGet performs a Bearer-authenticated GET — used by Google. Facebook
+// uses plainGet with the token in a query param instead.
 func httpGet(ctx context.Context, tok *oauth2.Token, url string) ([]byte, error) {
 	cli := oauth2.NewClient(ctx, oauth2.StaticTokenSource(tok))
 	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)