Password authentication methods in PostgreSQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding PostgreSQL password authentication methods

Which PostgreSQL password authentication method stores passwords in a hashed format using MD5 and requires the client to send an MD5-hashed password for verification?

A password

B md5

C trust

D peer

💡 Hint

Think about which method hashes the password before sending it over the network.

The md5 method stores passwords hashed with MD5 and requires the client to send an MD5 hash of the password, providing better security than sending plain text.

❓ query_result

intermediate

Result of authentication method in pg_hba.conf

Given the following line in pg_hba.conf:

host all all 192.168.1.0/24 scram-sha-256

What does this configuration enforce for connections from the 192.168.1.0/24 network?

A Requires SCRAM-SHA-256 password authentication

B Allows connections without password

C Allows only local socket connections

D Requires password sent in clear text

💡 Hint

Look at the authentication method specified at the end of the line.

The scram-sha-256 method requires clients to authenticate using the SCRAM-SHA-256 password mechanism, which is more secure than MD5.

📝 Syntax

advanced

Identify the syntax error in pg_hba.conf entry

Which of the following pg_hba.conf lines contains a syntax error?

A host all all 10.0.0.0/8 md5

B local all all trust

C hostssl all all 0.0.0.0/0 scram-sha-256

D host all all 192.168.1.0/24 password md5

💡 Hint

Check the order and validity of authentication methods in the line.

Option D incorrectly combines two authentication methods password and md5. Only one method should be specified.

❓ optimization

advanced

Optimizing password authentication for security and performance

You want to configure PostgreSQL to use the most secure password authentication method that is widely supported by clients, while minimizing performance overhead. Which method should you choose?

A scram-sha-256

B password

C md5

D trust

💡 Hint

Consider modern security standards and client support.

scram-sha-256 is the most secure widely supported method, providing strong password hashing and challenge-response authentication with reasonable performance.

🔧 Debug

expert

Debugging failed password authentication with SCRAM-SHA-256

A PostgreSQL server is configured to use scram-sha-256 authentication in pg_hba.conf. A client attempts to connect but receives an authentication failure. Which of the following is the most likely cause?

A The <code>pg_hba.conf</code> file is missing the <code>hostssl</code> keyword

B The client is connecting over a local socket

C The user's password is stored using MD5 hashing, not SCRAM-SHA-256

D The server is running on an unsupported PostgreSQL version

💡 Hint

Think about password storage format compatibility with authentication method.

If the user's password is stored as an MD5 hash, SCRAM-SHA-256 authentication will fail because it requires passwords stored in SCRAM format.

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