Password authentication methods in PostgreSQL - Step-by-Step Execution

Concept Flow - Password authentication methods

Client connects to server

↓

Server requests password

↓

Client sends password

↓

Server checks password method

↓

Compare password using method

↓

If match?

No→Reject connection

Yes↓

Allow connection

The client connects and sends a password. The server checks the password using the configured method. If it matches, connection is allowed; otherwise, rejected.

Execution Sample

PostgreSQL

CREATE USER alice WITH PASSWORD 'secret';
-- Client connects
-- Server uses md5 method
-- Password checked
-- Connection allowed if match

This example shows a user created with a password. When connecting, PostgreSQL uses the md5 method to verify the password.

Execution Table

Step	Action	Password Method	Password Sent	Check Result	Connection Status
1	Client connects	md5	sent hashed password	pending	pending
2	Server receives password	md5	received hashed password	compare hash	pending
3	Server compares password	md5	hashed password	match	pending
4	Password matches?	md5	hashed password	Yes	allow connection
5	Connection established	md5	hashed password	confirmed	connected

💡 Password matches using md5 method, connection allowed

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
password_method	undefined	md5	md5	md5	md5
password_sent	none	hashed password	hashed password	hashed password	hashed password
check_result	none	pending	compare hash	match	match
connection_status	disconnected	pending	pending	pending	connected

Key Moments - 2 Insights

Why does the server compare a hashed password instead of the plain password?

Because the md5 method stores and checks hashed passwords for security, as shown in execution_table step 2 and 3.

What happens if the password does not match?

The connection is rejected immediately after the check fails, as indicated by the 'Password matches?' decision in execution_table step 4.

Visual Quiz - 3 Questions

Look at the execution_table, what is the connection status at step 3?

A pending

B connected

C disconnected

D rejected

💡 Hint

Check the 'Connection Status' column at step 3 in the execution_table.

At which step does the server confirm the password matches?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look for the 'Password matches?' decision in the execution_table.

If the password method changed to 'scram-sha-256', what would change in the execution_table?

A Password Sent column would be empty

B Password Method column would show 'scram-sha-256'

C Connection Status would be 'rejected'

D No changes

💡 Hint

Focus on the 'Password Method' column in the execution_table.

Concept Snapshot

Password authentication in PostgreSQL:
- Client sends password on connect
- Server checks password using method (md5, scram-sha-256, etc.)
- Passwords are hashed for security
- Match allows connection; mismatch rejects
- Method set in pg_hba.conf or user creation

Full Transcript

When a client connects to PostgreSQL, the server requests a password. The client sends the password, usually hashed depending on the method. The server compares the received password with the stored one using the configured authentication method, such as md5 or scram-sha-256. If the password matches, the connection is allowed; otherwise, it is rejected. This process ensures secure authentication by never sending plain passwords over the network. The method used is configured in the server settings and can vary per user or connection type.

Practice

1. Which password authentication method in PostgreSQL is considered more secure and recommended for use?

easy

A. scram-sha-256

B. md5

C. password

D. trust

Solution

1. Step 1: Understand common PostgreSQL password methods

   PostgreSQL supports several password authentication methods including md5 and scram-sha-256.

2. Step 2: Compare security levels

   SCRAM-SHA-256 is a newer, more secure method than MD5, which is older and less secure.

3. Final Answer:

   scram-sha-256 -> Option A

4. Quick Check:

   More secure method = scram-sha-256 [OK]

Hint: SCRAM is newer and stronger than MD5 for passwords [OK]

Common Mistakes:

• Confusing md5 as more secure than scram-sha-256
• Choosing 'password' which sends plain text
• Selecting 'trust' which requires no password

2. Which line correctly sets password authentication to SCRAM in the pg_hba.conf file?

easy

A. host all all 0.0.0.0/0 password

B. host all all 0.0.0.0/0 md5

C. host all all 0.0.0.0/0 scram-sha-256

D. host all all 0.0.0.0/0 trust

Solution

1. Step 1: Identify the correct authentication method syntax

   The pg_hba.conf file uses lines like 'host all all address method' to set authentication.

2. Step 2: Match method to SCRAM

   To use SCRAM, the method must be exactly 'scram-sha-256'.

3. Final Answer:

   host all all 0.0.0.0/0 scram-sha-256 -> Option C

4. Quick Check:

   SCRAM method line = host all all 0.0.0.0/0 scram-sha-256 [OK]

Hint: SCRAM method is 'scram-sha-256' exactly in pg_hba.conf [OK]

Common Mistakes:

• Using 'md5' instead of 'scram-sha-256' for SCRAM
• Confusing 'password' with SCRAM
• Omitting the IP address or using wrong format

3. Given this pg_hba.conf line: host all all 192.168.1.0/24 md5, what happens when a user connects from IP 192.168.1.15?

medium

A. The user must use SCRAM authentication.

B. The user connects without a password.

C. The connection is rejected automatically.

D. The user must provide a password hashed with MD5 to authenticate.

Solution

1. Step 1: Analyze the IP range and method

   The line applies to IPs in 192.168.1.0/24, which includes 192.168.1.15, and uses md5 authentication.

2. Step 2: Understand md5 authentication behavior

   MD5 requires the client to send an MD5-hashed password for authentication.

3. Final Answer:

   The user must provide a password hashed with MD5 to authenticate. -> Option D

4. Quick Check:

   IP in range + md5 method = MD5 password required [OK]

Hint: MD5 method means password hashed with MD5 is required [OK]

Common Mistakes:

• Assuming SCRAM is used instead of MD5
• Thinking no password is needed
• Believing connection is rejected without password

4. You set host all all 0.0.0.0/0 scram-sha-256 in pg_hba.conf but users still connect without password prompts. What is the likely cause?

medium

A. The scram-sha-256 method is misspelled

B. PostgreSQL was not reloaded after changing pg_hba.conf

C. Users have no passwords set in the database

D. The IP address range is incorrect

Solution

1. Step 1: Check if configuration changes are active

   Changes to pg_hba.conf require PostgreSQL reload to take effect.

2. Step 2: Identify why password prompts are missing

   If users connect without password prompts, likely the new method is not active due to missing reload.

3. Final Answer:

   PostgreSQL was not reloaded after changing pg_hba.conf -> Option B

4. Quick Check:

   Config changes need reload = missing reload causes issue [OK]

Hint: Always reload PostgreSQL after pg_hba.conf changes [OK]

Common Mistakes:

• Assuming misspelling causes no prompt instead of error
• Ignoring need to reload server
• Thinking IP range affects password prompt

5. You want to enforce SCRAM authentication only for users connecting from the local network (192.168.0.0/16) and allow password authentication (md5) for others. Which two lines in pg_hba.conf achieve this correctly?

hard

A. host all all 192.168.0.0/16 scram-sha-256
host all all 0.0.0.0/0 md5

B. host all all 0.0.0.0/0 scram-sha-256
host all all 192.168.0.0/16 md5

C. host all all 192.168.0.0/16 md5
host all all 0.0.0.0/0 scram-sha-256

D. host all all 0.0.0.0/0 trust
host all all 192.168.0.0/16 scram-sha-256

Solution

1. Step 1: Understand pg_hba.conf line order and matching

   PostgreSQL checks lines top to bottom and uses the first matching rule.

2. Step 2: Set SCRAM for local network first, then md5 for others

   Line 1: local network with scram-sha-256; Line 2: all others with md5.

3. Final Answer:

   host all all 192.168.0.0/16 scram-sha-256 host all all 0.0.0.0/0 md5 -> Option A

4. Quick Check:

   Specific local network first, then general others [OK]

Hint: Put specific IP range first, general last in pg_hba.conf [OK]

Common Mistakes:

• Reversing line order causing wrong method to apply
• Using 'trust' which disables password
• Assigning md5 to local network instead of SCRAM