Storage access keys and SAS tokens in Azure - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Storage Access Key in Azure Storage?

A Storage Access Key is a secret key that grants full access to all data in an Azure Storage account. It acts like a master password to manage and access storage resources.

beginner

What does SAS stand for and what is its purpose?

SAS stands for Shared Access Signature. It allows you to grant limited and time-bound access to Azure Storage resources without sharing the storage account keys.

intermediate

How does a SAS token improve security compared to using Storage Access Keys directly?

A SAS token limits access by specifying permissions, resource types, and expiration time, reducing risk if the token is exposed. Storage Access Keys provide full access without restrictions.

intermediate

Name two types of SAS tokens in Azure Storage.

1. User Delegation SAS - uses Azure Active Directory credentials for enhanced security. 2. Service SAS - grants access based on storage account keys.

beginner

Why should you avoid sharing Storage Access Keys directly?

Because Storage Access Keys provide full control over the storage account, sharing them increases risk of unauthorized access. Using SAS tokens is safer as they limit permissions and duration.

What does a Shared Access Signature (SAS) token allow you to do?

A Reset the storage account keys

B Provide full access to the storage account

C Grant limited, time-bound access to storage resources

D Encrypt data in the storage account

A SAS token grants limited and time-bound access to storage resources without exposing full account keys.

Which of the following is a risk of sharing Storage Access Keys directly?

A Unauthorized full access to storage account

B Automatic expiration of access

C Limited access to specific files

D Access only to read data

Storage Access Keys provide full access, so sharing them risks unauthorized full control.

What is a User Delegation SAS?

A A SAS token signed with storage account keys

B A tool to encrypt storage data

C A key to reset storage account passwords

D A SAS token signed with Azure AD credentials

User Delegation SAS tokens are signed using Azure Active Directory credentials for better security.

Which permission can you NOT restrict with a SAS token?

A Write access

B Reset storage account keys

C Delete access

D Read access

SAS tokens cannot reset storage account keys; that requires full access via Storage Access Keys.

Why is it best practice to use SAS tokens instead of Storage Access Keys for sharing access?

A SAS tokens provide limited, revocable access

B Storage Access Keys only allow read access

C Storage Access Keys are free to share

D SAS tokens never expire

SAS tokens limit access scope and duration, making them safer for sharing.

Explain the difference between Storage Access Keys and SAS tokens in Azure Storage.

Think about access scope and security risks.

Describe scenarios where you would use a SAS token instead of a Storage Access Key.

Consider safety and control when sharing access.

Practice

1. What is the main difference between a storage access key and a SAS token in Azure Storage?

easy

A. SAS tokens provide full access; storage access keys provide limited access.

B. Both provide full access but SAS tokens expire faster.

C. Storage access keys provide full access; SAS tokens provide limited, temporary access.

D. Storage access keys are only for blobs; SAS tokens are for all storage types.

Solution

1. Step 1: Understand storage access keys

   Storage access keys give full control over the entire storage account without restrictions.

2. Step 2: Understand SAS tokens

   SAS tokens grant limited, time-bound access to specific resources or actions within the storage account.

3. Final Answer:

   Storage access keys provide full access; SAS tokens provide limited, temporary access. -> Option C

4. Quick Check:

   Access scope = Full vs Limited [OK]

Hint: Full control = access keys; limited control = SAS tokens [OK]

Common Mistakes:

• Confusing SAS tokens as full access keys
• Thinking SAS tokens never expire
• Assuming access keys are resource-specific

2. Which of the following is the correct way to generate a SAS token for a blob container using Azure CLI?

easy

A. az storage blob generate-sas --container-name mycontainer --permissions rwl --expiry 2024-12-31T23:59:00Z --account-name mystorage

B. az storage container generate-sas --name mycontainer --permissions rwl --expiry 2024-12-31T23:59:00Z --account-name mystorage

C. az storage account generate-sas --name mycontainer --permissions rwl --expiry 2024-12-31T23:59:00Z

D. az storage generate-sas --container mycontainer --permissions rwl --expiry 2024-12-31T23:59:00Z

Solution

1. Step 1: Identify the correct Azure CLI command for container SAS

   The command to generate a SAS token for a container is az storage container generate-sas.

2. Step 2: Check parameters

   az storage container generate-sas --name mycontainer --permissions rwl --expiry 2024-12-31T23:59:00Z --account-name mystorage correctly uses container name, permissions, expiry, and account name parameters.

3. Final Answer:

   az storage container generate-sas --name mycontainer --permissions rwl --expiry 2024-12-31T23:59:00Z --account-name mystorage -> Option B

4. Quick Check:

   Correct CLI command and parameters [OK]

Hint: Use 'container generate-sas' for containers, not 'blob generate-sas' [OK]

Common Mistakes:

• Using 'az storage blob generate-sas' for containers
• Omitting required parameters like --account-name
• Using incorrect command syntax

3. Given this SAS token snippet for a blob: ?sv=2023-01-01&ss=b&srt=sco&sp=rl&se=2024-07-01T00:00:00Z&st=2024-06-01T00:00:00Z&spr=https&sig=abc123, what permissions does it grant?

medium

A. Read and List permissions on blob service

B. Read and Write permissions on blob service

C. Full control on storage account

D. Only write permission on blob service

Solution

1. Step 1: Decode the SAS token parameters

   sp=rl means permissions are Read (r) and List (l).

2. Step 2: Understand service and resource types

   ss=b means the service is Blob storage.

3. Final Answer:

   Read and List permissions on blob service -> Option A

4. Quick Check:

   sp=rl means Read+List [OK]

Hint: Check 'sp' parameter for permissions letters [OK]

Common Mistakes:

• Confusing 'rl' with read-write
• Assuming full control from SAS token
• Ignoring service type 'ss' parameter

4. You created a SAS token with --permissions rwd but users report they cannot delete blobs. What is the likely cause?

medium

A. The SAS token lacks the 'Delete' permission 'x'.

B. The SAS token expired before use.

C. The storage account keys were regenerated.

D. The SAS token was generated for the wrong resource type.

Solution

1. Step 1: Understand permissions for delete

   Delete permission is represented by 'd', so 'rwd' includes delete.

2. Step 2: Check resource type relevance

   If the SAS token is generated for a container but used on blobs, or vice versa, permissions may not apply correctly.

3. Final Answer:

   The SAS token was generated for the wrong resource type. -> Option D

4. Quick Check:

   Permissions + resource type must match [OK]

Hint: Match SAS token resource type with intended use [OK]

Common Mistakes:

• Assuming 'x' is delete permission
• Ignoring resource type mismatch
• Not checking token expiry

5. You want to allow a third-party app to upload files to a specific blob container for 2 hours without exposing your storage account keys. Which approach is best?

hard

A. Generate a SAS token scoped to the container with write permission and 2-hour expiry.

B. Create a new storage account for the app.

C. Share the storage account access keys with the app.

D. Use a SAS token with full permissions and no expiry.

Solution

1. Step 1: Avoid sharing storage account keys

   Sharing keys gives full control and is insecure for third parties.

2. Step 2: Use SAS token with limited scope and expiry

   Generating a SAS token scoped to the container with write permission and a 2-hour expiry limits access and duration.

3. Step 3: Evaluate other options

   Creating a new storage account is unnecessary overhead; SAS token with full permissions and no expiry is insecure.

4. Final Answer:

   Generate a SAS token scoped to the container with write permission and 2-hour expiry. -> Option A

5. Quick Check:

   Limited scope + expiry = SAS token best practice [OK]

Hint: Use SAS tokens for limited, timed access, not keys [OK]

Common Mistakes:

• Sharing full access keys with third parties
• Using SAS tokens without expiry
• Creating unnecessary storage accounts