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Boost Performance & Security: SAS Tokens for Azure Blob Uploads Over Service API

· 8 min read

As the digital landscape evolves, organizations are increasingly migrating to the cloud, seeking robust, scalable, and secure storage solutions. Microsoft Azure, a leading cloud service provider, offers Azure BLOB storage—a reliable platform for storing unstructured data like text, images, and binary files. However, traditional cloud storage architectures can introduce complexity and security risks, particularly in large-scale applications. To address these challenges, Azure’s Shared Access Signatures (SAS) provide a more streamlined and secure approach.

The Traditional Approach: A Complex and Risky Process​

Traditional Approach

In a conventional cloud architecture, when a user uploads a file through a web application, the file typically passes through an API layer before being stored in Azure BLOB storage. This API layer is responsible for validating the file, performing security checks, and then uploading the file to the cloud. While this architecture may suffice for on-premises applications, it introduces unnecessary complexity and potential security vulnerabilities when deployed in the cloud.

For instance, managing file uploads through an API can lead to increased latency, as files must be processed by the API before reaching the storage service. This architecture also increases the attack surface, as more components are involved in the process, each of which must be secured and maintained.

Azure Shared Access Signatures (SAS): A Streamlined Solution​

SAS

Azure's Shared Access Signatures (SAS) offer a more efficient and secure alternative to the traditional approach. A SAS is a URI that grants limited access to Azure Storage resources, allowing clients to perform operations such as uploading, downloading, or deleting files directly within Azure BLOB storage—without needing to pass through an intermediary API layer.

By using SAS, you can eliminate the complexity of the traditional architecture. Instead of routing files through an API, clients can interact directly with Azure BLOB storage using a pre-signed URL, known as a SAS token. This token specifies permissions, the time-to-live (TTL), and other security parameters, making the process both secure and straightforward.

Types of SAS Tokens​

Azure provides several types of SAS tokens, each catering to different use cases:

  • Account SAS: Grants access to resources within a storage account, allowing operations like uploading, downloading, and listing BLOBs.
  • Service SAS: Provides access to a specific service (e.g., BLOB, file, queue, or table) within the storage account.
  • User Delegation SAS: Generated using Azure Active Directory (AD) credentials, offering enhanced security by limiting access based on user identity.

How to Create SAS Tokens​

Creating SAS tokens in Azure is straightforward and can be done through various tools:

Azure Portal

Creating SAS (Shared Access Signature) tokens in Azure allows you to grant limited access to resources in a storage account without exposing the account key. Here’s a step-by-step guide to creating SAS tokens using Azure Portal and Azure CLI:

Method 1: Creating SAS Tokens via Azure Portal​

  1. Log in to Azure Portal:

  2. Navigate to your Storage Account:

    • In the Azure Portal, search for "Storage accounts" and select your storage account from the list.

  3. Access Shared Access Signature (SAS) Settings:

    • In the storage account blade, under the "Settings" section, click on Shared access signature.

  4. Configure SAS Token Options:

    • Allowed services: Choose the services that the SAS token will apply to (Blob, File, Queue, Table).
    • Allowed resource types: Select the resource types (Service, Container, Object) that the SAS will allow access to.
    • Allowed permissions: Select the permissions (Read, Write, Delete, List, etc.) that the SAS token will grant.
    • Start and Expiry date/time: Set the validity period for the SAS token.
    • Allowed IP addresses: (Optional) Specify a range of IP addresses from which the resources can be accessed.
    • Allowed protocols: Choose whether the SAS token can be used over HTTPS only or both HTTP and HTTPS.

  5. Generate the SAS Token and URL:

    • Once you've configured all the options, click on Generate SAS and connection string.
    • The portal will display the SAS token and the full URL, which includes the SAS token. Copy this for your use.

  6. Use the SAS Token:

    • You can use the generated SAS token in your applications to access the storage resources with the specified permissions.

Method 2: Creating SAS Tokens via Azure CLI​

  1. Install Azure CLI:

  2. Log in to Azure:

    • Open a command prompt or terminal and run az login to log in to your Azure account.

  3. Generate a SAS Token:

    • Use the az storage account generate-sas command to generate a SAS token. Here’s a basic example:
    az storage account generate-sas \
      --account-name <your-storage-account-name> \
      --expiry <expiry-date-time> \
      --permissions <permissions> \
      --resource-types <resource-types> \
      --services <services> \
      --https-only \
      --output tsv

    Example:

    az storage account generate-sas \
      --account-name mystorageaccount \
      --expiry 2024-09-01T00:00Z \
      --permissions rwdlacup \
      --resource-types sco \
      --services b \
      --https-only \
      --output tsv
    • Explanation:
      • --account-name: The name of your storage account.
      • --expiry: The expiry date and time for the SAS token in UTC format.
      • --permissions: The permissions (e.g., r for read, w for write, d for delete, etc.).
      • --resource-types: The resource types (Service s, Container c, Object o).
      • --services: The services (Blob b, File f, Queue q, Table t).
      • --https-only: (Optional) Ensures the SAS can only be used over HTTPS.
      • --output tsv: Outputs the SAS token in plain text.

  4. Use the SAS Token:

    • The output will be your SAS token, which you can append to your storage resource URL.

By following these steps, you can successfully create a SAS token that grants specific access to your Azure Storage resources.

Key Benefits of Using SAS in Azure​

1. Enhanced Security SAS tokens provide a secure way to grant limited access to your storage resources. By specifying a TTL, permissions, and other security parameters, you can ensure that access is both temporary and restricted to only the necessary operations.

2. Simplified Architecture With SAS, the need for an intermediary API to manage file uploads is eliminated, significantly reducing the complexity of your application’s architecture. This results in lower development and maintenance costs and a more streamlined deployment process.

3. Improved Performance Allowing clients to upload files directly to Azure BLOB storage using SAS tokens improves performance by reducing the latency associated with routing files through an API. This direct interaction ensures faster upload speeds and a more responsive application.

4. Cost Efficiency Simplifying your architecture by removing unnecessary components, such as an API layer, can lead to significant cost savings. Fewer resources are required to manage and maintain the system, resulting in lower operational costs.

5. Flexibility and Fine-Grained Access Control SAS tokens offer granular control over who can access your data and what they can do with it. You can create tokens that are valid for only a few minutes or extend their validity for longer periods, depending on your needs. This flexibility allows you to tailor access policies to the specific requirements of your application.

Best Practices for Using SAS Tokens​

To maximize the benefits of SAS tokens, it is important to follow best practices:

  • Implement Least Privilege: Grant only the minimum permissions necessary for the task at hand.
  • Use Short Lifetimes: Set the TTL of SAS tokens to the shortest possible duration, reducing the risk of unauthorized access.
  • Apply IP Restrictions: Limit access to specific IP ranges to prevent unauthorized access from unknown locations.
  • Enforce HTTPS: Always require HTTPS to ensure that data is transmitted securely.

Conclusion​

As cloud architectures continue to evolve, leveraging modern tools like Azure Shared Access Signatures (SAS) is crucial for building efficient, secure, and scalable applications. By using SAS, you can streamline your cloud storage processes, enhance security, and reduce costs—ultimately leading to a more agile and responsive business. Whether you’re migrating existing applications to the cloud or building new ones, incorporating SAS into your Azure strategy is a smart move that will pay dividends in the long run.

This blog post integrates insights from the provided audio and document, offering a comprehensive overview of SAS tokens in Azure and their benefits in cloud storage architecture.