Store signin data in DB and use random codes

schema.sql

@@ -1,4 +1,4 @@
-CREATE TABLE Players (
+CREATE TABLE IF NOT EXISTS Players (
   email TEXT PRIMARY KEY,
   username TEXT UNIQUE,
   digest BLOB,
@@ -7,3 +7,11 @@ CREATE TABLE Players (
   new_pass_code TEXT,
   created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
 );
+
+CREATE TABLE IF NOT EXISTS SignedInUsers (
+  code TEXT PRIMARY KEY,
+  player TEXT,
+  created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+  last_used_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+  FOREIGN KEY (player) REFERENCES Players (email) ON DELETE CASCADE
+);