add minimal solution

minimal_auth.py

@@ -0,0 +1,78 @@
+import json
+import pathlib
+import sys
+
+# name of the file where we store the pw database
+PWDB_FLNAME = pathlib.Path('pwdb.json')
+
+def get_credentials():
+    # get input from terminal
+    username = input('Enter your username: ')
+    # get password using the appropriate module, so that typed characters are not
+    # echoed to the terminal
+    password = input('Enter your password: ')
+    return (username, password)
+
+def authenticate(username, password, pwdb):
+    # calculate hash and compare with stored hash
+    return password == pwdb[username]
+
+def add_user(username, pwdb):
+    # do not try to add a username twice
+    if username in pwdb:
+        raise Exception(f'Username already exists [{username}]!')
+    else:
+         pwdb[username] = input(f'Enter password for {username}: ')
+    return pwdb
+
+def read_pwdb(pwdb_path):
+    # try to read from the database
+    # if anything happens, report the error!
+    if not pwdb_path.exists():
+        initialize_pwdb(pwdb_path)
+    try:
+        with open(pwdb_path, 'rt') as pwdb_file:
+            pwdb = json.load(pwdb_file)
+    except json.decoder.JSONDecodeError as exc:
+        # this happens when the json data is invalid
+        raise Exception(f'Invalid database {pwdb_path}: {exc}')
+    except Exception as exc:
+        # this is a catch-all condition
+        raise Exception(f'Unkown error reading {pwdb_path}: {exc}')
+    return pwdb
+
+def write_pwdb(pwdb, pwdb_path):
+    with open(pwdb_path, 'wt') as pwdb_file:
+        json.dump(pwdb, pwdb_file)
+
+def initialize_pwdb(pwdb_path):
+    write_pwdb({}, pwdb_path)
+
+def main(pwdb_path):
+    # load the password database from file
+    pwdb = read_pwdb(pwdb_path)
+
+    # if we are passed an argument, we want to add a new user
+    if len(sys.argv) > 1:
+        pwdb = add_user(sys.argv[1], pwdb)
+        write_pwdb(pwdb, pwdb_path)
+        return
+
+    # ask for credentials
+    username, password = get_credentials()
+
+    if username not in pwdb:
+        print('Wrong username!')
+        return
+
+    # try to authenticate
+    if authenticate(username, password, pwdb):
+        print('Successfully authenticated!')
+    else:
+        # report wrong password
+        print('Wrong password!')
+    return
+
+if __name__ == '__main__':
+    main(PWDB_FLNAME)
+