diff --git a/auth.py b/auth.py
new file mode 100644
index 0000000..67064e5
--- /dev/null
+++ b/auth.py
@@ -0,0 +1,42 @@
+import json
+import sys
+
+def get_credentials():
+    username = input('Enter your username: ')
+    password = input('Enter your password: ')
+    return (username, password)
+
+def authenticate(username, password, pwdb):
+    return password == pwdb[username]
+
+def add_user(username, pwdb):
+    pwdb[username] = input(f'Enter password for {username}: ')
+    return pwdb
+
+def read_pwdb(pwdb_path):
+    try:
+        pwdb_file = open(pwdb_path, 'rt')
+        pwdb = json.load(pwdb_file)
+    except Exception:
+        pwdb = {}
+    return pwdb
+
+def write_pwdb(pwdb, pwdb_path):
+    pwdb_file = open(pwdb_path, 'wt')
+    json.dump(pwdb, pwdb_file)
+
+pwdb_path = 'pwdb.json'
+pwdb = read_pwdb(pwdb_path)
+
+if len(sys.argv) > 1:
+    pwdb = add_user(sys.argv[1], pwdb)
+    write_pwdb(pwdb, pwdb_path)
+else:
+    username, password = get_credentials()
+    if username not in pwdb:
+        print('Wrong username!')
+    else:
+        if authenticate(username, password, pwdb):
+            print('Successfully authenticated!')
+        else:
+            print('Wrong password!')