diff --git a/app/account_linking.py b/app/account_linking.py
index 781d638c9..88ef1fbda 100644
--- a/app/account_linking.py
+++ b/app/account_linking.py
@@ -276,7 +276,7 @@ def process_link_case(
         return link_user(link_request, current_user, partner)
 
     # There is a SL user registered with the partner. Check if is the current one
-    if partner_user.id == current_user.id:
+    if partner_user.user_id == current_user.id:
         # Update plan
         set_plan_for_partner_user(partner_user, link_request.plan)
         # It's the same user. No need to do anything
@@ -285,5 +285,4 @@ def process_link_case(
             strategy="Link",
         )
     else:
-
         return switch_already_linked_user(link_request, partner_user, current_user)
diff --git a/app/auth/views/proton.py b/app/auth/views/proton.py
index 8e3551b41..52fa148a6 100644
--- a/app/auth/views/proton.py
+++ b/app/auth/views/proton.py
@@ -23,7 +23,7 @@
     Action,
 )
 from app.proton.utils import get_proton_partner
-from app.utils import sanitize_next_url
+from app.utils import sanitize_next_url, sanitize_scheme
 
 _authorization_base_url = PROTON_BASE_URL + "/oauth/authorize"
 _token_url = PROTON_BASE_URL + "/oauth/token"
@@ -34,6 +34,7 @@
 
 SESSION_ACTION_KEY = "oauth_action"
 SESSION_STATE_KEY = "oauth_state"
+DEFAULT_SCHEME = "auth.simplelogin"
 
 
 def get_api_key_for_user(user: User) -> str:
@@ -75,6 +76,12 @@ def proton_login():
     elif "oauth_next" in session:
         del session["oauth_next"]
 
+    scheme = sanitize_scheme(request.args.get("scheme"))
+    if scheme:
+        session["oauth_scheme"] = scheme
+    elif "oauth_scheme" in session:
+        del session["oauth_scheme"]
+
     mode = request.args.get("mode", "session")
     if mode == "apikey":
         session["oauth_mode"] = "apikey"
@@ -146,6 +153,7 @@ def check_status_code(response: requests.Response) -> requests.Response:
     handler = ProtonCallbackHandler(proton_client)
     proton_partner = get_proton_partner()
 
+    next_url = session.get("oauth_next")
     if action == Action.Login:
         res = handler.handle_login(proton_partner)
     elif action == Action.Link:
@@ -156,15 +164,17 @@ def check_status_code(response: requests.Response) -> requests.Response:
     if res.flash_message is not None:
         flash(res.flash_message, res.flash_category)
 
+    oauth_scheme = session.get("oauth_scheme")
     if session.get("oauth_mode", "session") == "apikey":
         apikey = get_api_key_for_user(res.user)
-        return redirect(f"auth.simplelogin://callback?apikey={apikey}")
+        scheme = oauth_scheme or DEFAULT_SCHEME
+        return redirect(f"{scheme}:///login_callback?apikey={apikey}")
 
     if res.redirect_to_login:
         return redirect(url_for("auth.login"))
 
-    if res.redirect:
-        return after_login(res.user, res.redirect, login_from_proton=True)
+    if next_url and next_url[0] == "/" and oauth_scheme:
+        next_url = f"{oauth_scheme}://{next_url}"
 
-    next_url = session.get("oauth_next")
-    return after_login(res.user, next_url, login_from_proton=True)
+    redirect_url = next_url or res.redirect
+    return after_login(res.user, redirect_url, login_from_proton=True)
diff --git a/app/proton/proton_callback_handler.py b/app/proton/proton_callback_handler.py
index dd504f6db..53c807631 100644
--- a/app/proton/proton_callback_handler.py
+++ b/app/proton/proton_callback_handler.py
@@ -64,7 +64,9 @@ def handle_login(self, partner: Partner) -> ProtonCallbackResult:
             )
 
     def handle_link(
-        self, current_user: Optional[User], partner: Partner
+        self,
+        current_user: Optional[User],
+        partner: Partner,
     ) -> ProtonCallbackResult:
         if current_user is None:
             raise Exception("Cannot link account with current_user being None")
diff --git a/app/utils.py b/app/utils.py
index ba5c8657e..4bf954422 100644
--- a/app/utils.py
+++ b/app/utils.py
@@ -1,3 +1,4 @@
+import re
 import secrets
 import string
 import time
@@ -88,6 +89,8 @@ def sanitize(url: Optional[str], allowed_domains: List[str]) -> Optional[str]:
             else:
                 return None
         if result.path and result.path[0] == "/" and not result.path.startswith("//"):
+            if result.query:
+                return f"{result.path}?{result.query}"
             return result.path
 
         return None
@@ -97,6 +100,17 @@ def sanitize_next_url(url: Optional[str]) -> Optional[str]:
     return NextUrlSanitizer.sanitize(url, ALLOWED_REDIRECT_DOMAINS)
 
 
+def sanitize_scheme(scheme: Optional[str]) -> Optional[str]:
+    if not scheme:
+        return None
+    if scheme in ["http", "https"]:
+        return None
+    scheme_regex = re.compile("^[a-z.]+$")
+    if scheme_regex.match(scheme):
+        return scheme
+    return None
+
+
 def query2str(query):
     """Useful utility method to print out a SQLAlchemy query"""
     return query.statement.compile(compile_kwargs={"literal_binds": True})