User authentication basics in Raspberry Pi - Step-by-Step Execution

Concept Flow - User authentication basics

Start

↓

User enters username

↓

User enters password

↓

Check if username exists

Yes/No↓

Check password

The flow shows how a system asks for username and password, checks them, and either grants or rejects access.

Execution Sample

Raspberry Pi

users = {'alice': '1234', 'bob': 'abcd'}
username = input('Username: ')
password = input('Password: ')
if username in users and users[username] == password:
    print('Access granted')
else:
    print('Access denied')

This code asks for username and password, then checks if they match stored data to allow or deny access.

Execution Table

Step	Action	Input/Check	Result	Output
1	Ask for username	User types 'alice'	username = 'alice'
2	Ask for password	User types '1234'	password = '1234'
3	Check if username in users	'alice' in users	True
4	Check if password matches	users['alice'] == '1234'	True
5	Decision	Both checks True	Access granted	Access granted
6	End	No more steps

💡 Access granted because username exists and password matches

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
username	''	'alice'	'alice'	'alice'	'alice'	'alice'
password	''	''	'1234'	'1234'	'1234'	'1234'

Key Moments - 2 Insights

Why do we check if the username exists before checking the password?

Because if the username is not in the stored users, checking the password would cause an error or be meaningless. Step 3 in the execution_table shows this check.

What happens if the password does not match the stored password?

The program prints 'Access denied' and does not grant access. This is shown in the else branch after step 4 in the execution_table.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of 'username' after step 2?

A '1234'

B ''

C 'alice'

D 'bob'

💡 Hint

Check the variable_tracker table under 'username' after step 2.

At which step does the program decide to grant access?

A Step 5

B Step 4

C Step 3

D Step 6

💡 Hint

Look at the 'Decision' action in the execution_table.

If the user types username 'bob' and password 'wrong', what will the output be?

A Access granted

B Access denied

C Error

D No output

💡 Hint

Refer to the key_moments explanation about password mismatch.

Concept Snapshot

User authentication basics:
- Ask user for username and password
- Check if username exists in stored data
- Verify password matches stored password
- Grant access if both checks pass
- Otherwise, deny access

Full Transcript

This example shows how a simple user authentication works on a Raspberry Pi. The program asks the user to enter a username and password. It then checks if the username exists in the stored users dictionary. If it does, it compares the entered password with the stored password. If both match, it prints 'Access granted'. Otherwise, it prints 'Access denied'. This process helps protect access to the system by verifying user identity.