fix(auth): set User-Agent on avatar fetch and sync avatar on link-account register (#37564) (#37588) (#37726)

Backport #37588 by @pandareen

## Summary

Fixes
[go-gitea/gitea#37564](https://github.com/go-gitea/gitea/issues/37564):
when an OIDC provider returns a `picture` claim, Gitea is supposed to
download that image as the user's avatar (if `[oauth2_client]
UPDATE_AVATAR = true`). Two latent bugs prevented this from working
consistently:

1. **Default Go User-Agent rejected by some image hosts.**
`oauth2UpdateAvatarIfNeed` used `http.Get`, which sends `User-Agent:
Go-http-client/1.1`. Hosts like `upload.wikimedia.org` reject that UA
with `403`, and every error path silently returned, so the user was left
with an identicon and **no log line** to diagnose the issue.
2. **Link-account *register* path skipped avatar sync.** First-time OIDC
sign-ins where auto-registration is disabled (or required a
username/password retype) go through `LinkAccountPostRegister`, which
created the user but never called `oauth2SignInSync`. So the avatar /
full name / SSH keys from the IdP were dropped on the floor for those
users, even though the existing-account-link path (`oauth2LinkAccount`)
and the auto-register path (`handleOAuth2SignIn`) both already did the
sync.

## Changes

- `routers/web/auth/oauth.go` — `oauth2UpdateAvatarIfNeed` now uses
`http.NewRequest` + `http.DefaultClient.Do`, sets `User-Agent: Gitea
<version>`, and logs every failure path at `Warn` (invalid URL, fetch
error, non-200, body read error, oversize body, upload error). No silent
failures.
- `routers/web/auth/linkaccount.go` — `LinkAccountPostRegister` now
calls `oauth2SignInSync` after a successful user creation, mirroring the
auto-register and link-existing-account flows.
- `tests/integration/oauth_avatar_test.go` — new
`TestOAuth2AvatarFromPicture` integration test with five sub-cases:
- `AutoRegister_FetchesAvatarFromPictureWithGiteaUA` — happy path,
asserts `use_custom_avatar=true`, an avatar hash is set, exactly one
HTTP request was made, and the request carried a `Gitea ` UA. The mock
server enforces the UA prefix to mirror real-world hosts that reject
Go's default UA.
- `AutoRegister_NonOK_DoesNotUpdateAvatar` — server returns 403; user's
avatar must remain unset.
- `AutoRegister_EmptyPicture_NoFetch` — empty `picture` claim must not
trigger any HTTP request.
- `AutoRegister_UpdateAvatarFalse_NoFetch` — `UPDATE_AVATAR=false` must
not trigger any HTTP request.
- `LinkAccountRegister_FetchesAvatarFromPicture` — guards the
`linkaccount.go` fix; without the new `oauth2SignInSync` call this
assertion fails.

## Test plan

- [x] `go test -tags 'sqlite sqlite_unlock_notify' -run
'^TestOAuth2AvatarFromPicture$' ./tests/integration/ -v` — 5/5 sub-tests
pass.
- [x] Manual: log in as a Keycloak user with `picture` claim pointing at
`https://avatars.githubusercontent.com/u/9919?v=4` — Gitea avatar is
replaced with the GitHub picture.
- [x] Manual: same flow with `https://upload.wikimedia.org/...` —
request now succeeds (or returns a clearly logged `Warn` line if
rate-limited with `429`); previously it silently 403'd.
- [x] Manual: `UPDATE_AVATAR=false` — user keeps the identicon, no
outbound request in container logs.
- [ ] Reviewer: please double-check that no other call sites of
`oauth2UpdateAvatarIfNeed` rely on the old `http.Get` behaviour.

## Related

- Upstream issue: go-gitea/gitea#37564
--------------------------------------------


AI Editor was used in this PR

---------

Signed-off-by: silverwind <me@silverwind.io>
Co-authored-by: pandareen <7270563+pandareen@users.noreply.github.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Claude (Opus 4.7) <noreply@anthropic.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Nicolas <bircni@icloud.com>

routers/web/auth/linkaccount.go

@@ -263,6 +263,11 @@ func LinkAccountPostRegister(ctx *context.Context) {
 		return
 	}
 
+	oauth2SignInSync(ctx, linkAccountData.AuthSourceID, u, linkAccountData.GothUser)
+	if ctx.Written() {
+		return
+	}
+
 	authSource, err := auth.GetSourceByID(ctx, linkAccountData.AuthSourceID)
 	if err != nil {
 		ctx.ServerError("GetSourceByID", err)

routers/web/auth/oauth.go

@@ -13,6 +13,7 @@ import (
 	"net/url"
 	"sort"
 	"strings"
+	"time"
 
 	"code.gitea.io/gitea/models/auth"
 	user_model "code.gitea.io/gitea/models/user"
@@ -301,21 +302,42 @@ func showLinkingLogin(ctx *context.Context, authSourceID int64, gothUser goth.Us
 	ctx.Redirect(setting.AppSubURL + "/user/link_account")
 }
 
-func oauth2UpdateAvatarIfNeed(ctx *context.Context, url string, u *user_model.User) {
-	if setting.OAuth2Client.UpdateAvatar && len(url) > 0 {
-		resp, err := http.Get(url)
-		if err == nil {
-			defer func() {
-				_ = resp.Body.Close()
-			}()
-		}
-		// ignore any error
-		if err == nil && resp.StatusCode == http.StatusOK {
-			data, err := io.ReadAll(io.LimitReader(resp.Body, setting.Avatar.MaxFileSize+1))
-			if err == nil && int64(len(data)) <= setting.Avatar.MaxFileSize {
-				_ = user_service.UploadAvatar(ctx, u, data)
-			}
-		}
+var oauth2AvatarHTTPClient = &http.Client{Timeout: 30 * time.Second}
+
+func oauth2UpdateAvatarIfNeed(ctx *context.Context, avatarURL string, u *user_model.User) {
+	if !setting.OAuth2Client.UpdateAvatar || len(avatarURL) == 0 {
+		return
+	}
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, avatarURL, nil)
+	if err != nil {
+		log.Warn("invalid avatar URL %q: %v", avatarURL, err)
+		return
+	}
+	// Some hosts (e.g. Wikimedia) reject Go's default User-Agent.
+	req.Header.Set("User-Agent", "Gitea "+setting.AppVer)
+
+	resp, err := oauth2AvatarHTTPClient.Do(req)
+	if err != nil {
+		log.Warn("fetch %q failed: %v", avatarURL, err)
+		return
+	}
+	defer func() { _ = resp.Body.Close() }()
+
+	if resp.StatusCode != http.StatusOK {
+		log.Warn("fetch %q returned status %d", avatarURL, resp.StatusCode)
+		return
+	}
+	data, err := io.ReadAll(io.LimitReader(resp.Body, setting.Avatar.MaxFileSize+1))
+	if err != nil {
+		log.Warn("read body from %q failed: %v", avatarURL, err)
+		return
+	}
+	if int64(len(data)) > setting.Avatar.MaxFileSize {
+		log.Warn("avatar from %q exceeds max size %d", avatarURL, setting.Avatar.MaxFileSize)
+		return
+	}
+	if err := user_service.UploadAvatar(ctx, u, data); err != nil {
+		log.Warn("UploadAvatar for user %q failed: %v", u.Name, err)
 	}
 }