diff --git a/src/bapi/blueprints/discord.py b/src/bapi/blueprints/discord.py
index 173f5ec..3f833d3 100644
--- a/src/bapi/blueprints/discord.py
+++ b/src/bapi/blueprints/discord.py
@@ -1,4 +1,5 @@
 import ipaddress
+import re
 import secrets
 import urllib.parse
 
@@ -26,18 +27,22 @@
 @discord_blueprint.route("/auth", methods=["GET"])
 def discord_auth():
     ip = request.args.get("ip")
+    ip_str = None
     if not isinstance(ip, str):
         return jsonify({"error": "provided IP address invalid"}), 400
     try:
+        ip_str = ip
         ip = ipaddress.ip_address(ip)
     except ValueError:
         return jsonify({"error": "provided IP address invalid"}), 400
+    if "," in ip_str:
+        return jsonify({"error": "provided IP address invalid"}), 400
     if ip.version == 6:
         return jsonify({"error": "IPv6 address not allowed"}), 400
     if ip.is_multicast or ip.is_unspecified:
         return jsonify({"error": "multicast or unspecified address not allowed"}), 400
     seeker_port = request.args.get("seeker_port")
-    if not isinstance(seeker_port, str) or not seeker_port.isdigit():
+    if not isinstance(seeker_port, str) or not re.match("^[0-9]+$", seeker_port):
         seeker_port = ""
     try:
         seeker_port = int(seeker_port)
@@ -45,8 +50,11 @@ def discord_auth():
         seeker_port = ""
     if not isinstance(seeker_port, int) or seeker_port > 65535 or seeker_port < 1023:
         seeker_port = ""
+    nonce = request.args.get("nonce")
+    if not isinstance(nonce, str) or len(nonce) != 64 or not re.match("^[a-z0-9]+$", nonce):
+        return jsonify({"error": "bad nonce"}), 400
     session["oauth2_state"] = (
-        f"{urllib.parse.quote(ip.exploded, safe="", encoding="utf-8")},{seeker_port},{secrets.token_urlsafe(16)}"
+        f"{urllib.parse.quote(ip_str, safe="", encoding="utf-8")},{seeker_port},{nonce},{secrets.token_urlsafe(16)}"
     )
     return redirect(discord_client.generate_uri(scope=["identify"], state=session["oauth2_state"]))
 
@@ -65,8 +73,34 @@ def discord_callback():
     del session["oauth2_state"]
 
     state_attrs = state.split(",")
+    if len(state_attrs) != 4:
+        return jsonify({"error": "bad state"}), 400
     ip = urllib.parse.unquote(state_attrs[0])
-    seeker_port = state_attrs[1]
+    try:
+        seeker_port = int(state_attrs[1])
+    except ValueError:
+        return jsonify({"error": "bad state"}), 400
+    nonce = state_attrs[2]
+    if not isinstance(nonce, str) or len(nonce) != 64 or not re.match("^[a-z0-9]+$", nonce):
+        return jsonify({"error": "bad state"}), 400
+    nonce_duration = cfg.API.get("nonce-valid-duration")
+    if nonce_duration is None:
+        nonce_duration = 240
+    try:
+        nonce_valid, reason_invalid = db.SessionCreationNonce.is_valid_session_creation(
+            ip, seeker_port, nonce, nonce_duration
+        )
+        if not nonce_valid:
+            notice = ""
+            if reason_invalid == "invalid":
+                notice = " account security risk: check if connected to a genuine BeeStation game server."
+            elif reason_invalid == "expired":
+                notice = " log in within a shorter time period."
+            return jsonify({"error": f"{reason_invalid or "invalid"} nonce.{notice}"}), 401
+    except Exception as e:
+        current_app.logger.error(f"error while checking nonce: {e}")
+        return jsonify({"error": "error checking nonce"}), 500
+
     discord_uid = None
     discord_username = None
 
diff --git a/src/bapi/config/api.yml b/src/bapi/config/api.yml
index 23e671e..d9706c7 100644
--- a/src/bapi/config/api.yml
+++ b/src/bapi/config/api.yml
@@ -6,3 +6,4 @@ api-url: "https://api.beestation13.com"
 
 request-source: "bapi"
 game-session-duration: 90 # valid duration of created game session tokens, in days.
+nonce-valid-duration: 240 # valid duration of a session creation nonce, in seconds.
diff --git a/src/bapi/db.py b/src/bapi/db.py
index 0f25c8d..eb84ebf 100644
--- a/src/bapi/db.py
+++ b/src/bapi/db.py
@@ -15,6 +15,7 @@
 from sqlalchemy import SmallInteger
 from sqlalchemy import String
 from sqlalchemy import Text
+from sqlalchemy.orm import column_property
 from sqlalchemy.orm.exc import NoResultFound
 from sqlalchemy.sql.expression import text
 
@@ -55,6 +56,38 @@ def create_session(cls, ip, external_method, external_uid, external_display_name
         return random_token
 
 
+class SessionCreationNonce(sqlalchemy_ext.Model):
+    __bind_key__ = "session"
+    __tablename__ = "SS13_session_creation_nonce"
+
+    created = Column("created", DateTime())
+    id = Column("id", Integer(), primary_key=True)
+    ip = Column("ip", String(32))
+    session_nonce = Column("session_nonce", String(64))
+    seeker_port = Column("seeker_port", Integer())
+    seconds_since_creation = column_property(func.timestampdiff(text("SECOND"), created, func.now()))
+
+    @classmethod
+    def is_valid_session_creation(cls, ip, seeker_port, nonce, valid_duration):
+        valid_nonce = None
+        try:
+            valid_nonce = (
+                db_session.query(cls)
+                .filter(and_(cls.session_nonce == nonce, cls.ip == ip, cls.seeker_port == seeker_port))
+                .one()
+            )
+        except NoResultFound:
+            return (False, "invalid")
+        if valid_nonce is None:
+            return (False, "invalid")
+        else:
+            db_session.delete(valid_nonce)
+            print(valid_nonce.seconds_since_creation)
+            if valid_nonce.seconds_since_creation > (valid_duration or 240):
+                return (False, "expired")
+            return (True, "")
+
+
 class Player(sqlalchemy_ext.Model):
     __bind_key__ = "game"
     __tablename__ = "SS13_player"