Cross-Origin Resource Sharing (CORS) is a standard that allows a server to interact with and determine how to handle requests from different origins. CORS specifically pertains to making HTTP requests from one domain to different domain. This is a security measure to prevent servers from having to accept all requests from all origins.
When you’re using JavaScript clients like a single page application or a browser-side JavaScript that accesses an API in a Microsoft Azure service like Cosmos DB, you might encounter some problems due to same-origin policy – a web security concept that restricts how a document or script from one origin can interact with a resource from another origin. This is where the importance of CORS comes in.
By configuring CORS settings, we can manage how our system and data handle requests from other origins, allowing safe and controlled cross-origin HTTP requests.
Configuring CORS in Azure Cosmos DB
In Azure Cosmos DB, the CORS policy can be configured at the account level. This means that if you set a CORS policy on an account, it applies to all the APIs, data, and containers in that account. This provides a blanket security measure that does not require per-API or per-database configuration.
To configure the CORS settings in Azure Cosmos DB, you would need to make use of Azure portal, Azure CLI, or Azure SDKs to implement the settings.
Using Azure Portal
Here’s how you can take advantage of Azure portal to set up your CORS rules:
- Log in to Azure portal.
- Navigate to Cosmos DB and select the account where you want to configure CORS.
- In the left-side menu, select ‘CORS’
- In the CORS settings page, you can add your origins (domains) separated by commas. You can also configure allowed headers, methods etc.
- After entering your settings, click on ‘Save’
Using Azure CLI or Azure SDK
In addition to Azure portal, you can configure CORS using Azure CLI or Azure SDK. Here is an example on how to set CORS rules using Azure CLI:
az cosmosdb update \
--name MyCosmosDBAccount \
--resource-group MyResourceGroup \
--allowed-origins http://example.com http://microsoft.com
In this command, replace `MyCosmosDBAccount` and `MyResourceGroup` with your Azure Cosmos DB account name and your resource group name respectively. Also, replace `http://example.com http://microsoft.com` with your origin(s). The origins are space separated.
When it comes to Azure SDKs, the command is based on the specific language being used, and the examples can be found in Microsoft Documentation.
It’s worth noting that in the list of allowed origins, if any URL contains a trailing ‘/’, the URL needs to be an exact match of the source origin. If the URL does not contain a trailing ‘/’, then all the subdomains of that origin are considered valid. Therefore, it’s imperative to ensure the URLs have been correctly implemented to avoid any potential issues that may arise.
Conclusion
Setting up CORS is an important step in securing your Azure Cosmos DB and ensuring effective interaction with different origins. It allows for safe and controlled access to the data stored in your Cosmos DB account. The process, as outlined here, is straightforward using Azure portal, Azure CLI, or Azure SDKs. It’s always best practice to review and refine your CORS settings regularly to ensure optimal security.
Practice Test
True/False: CORS is a mechanism that allows many resources (e.g., fonts, JavaScript, etc.) on a web page to be requested from another domain outside the domain from which the resource originated.
- True
- False
Answer: True
Explanation: CORS stands for Cross-Origin Resource Sharing. It enables resource sharing from a different domain, hence the statement is true.
Does Microsoft Azure Cosmos DB support Cross-Origin Resource Sharing (CORS)?
- A. Yes
- B. No
Answer: A. Yes
Explanation: Yes, Microsoft Azure Cosmos DB does support CORS. It allows web applications to bypass the same-origin policy, which enables secure cross-domain data transfer.
True/False: Microsoft Azure Cosmos DB does not support Configuration of CORS settings.
- True
- False
Answer: False
Explanation: Microsoft Azure Cosmos DB does support Configuration of CORS settings which can be set up from Azure portal.
Which HTTP headers does CORS mechanism use?
- A. DELETE
- B. OPTIONS
- C. PATCH
- D. ACCESS-CONTROL-REQUEST-METHOD
Answer: D. ACCESS-CONTROL-REQUEST-METHOD
Explanation: In CORS mechanism, the ACCESS-CONTROL-REQUEST-METHOD header is used to ensure a request is safe for certain data.
Which of the following services use CORS policy?
- A. Azure Cosmos DB
- B. Amazon S3
- C. Google Firebase
- D. All of the Above
Answer: D. All of the Above
Explanation: All these services i.e., Azure Cosmos DB, Amazon S3, Google Firebase support CORS policy and allow developers to configure CORS settings.
True/False: You can configure CORS settings for each platform separately in Azure Cosmos DB.
- True
- False
Answer: True
Explanation: Azure Cosmos DB allows configuring CORS settings for each platform separately which includes HTTP/HTTPS, TCP etc.
In CORS, what does the preflight request do?
- A. Sends Data
- B. Checks the Server’s CORS compliance
- C. Encrypts Data
- D. None of the above
Answer: B. Checks the Server’s CORS compliance
Explanation: Preflight request is used to check whether the server’s CORS policy allows the actual request from the client.
Which API does not support CORS in Azure Cosmos DB?
- A. SQL API
- B. MongoDB API
- C. Cassandra API
- D. All of them support CORS
Answer: D. All of them support CORS
Explanation: Azure Cosmos DB provides support for CORS in all its APIs i.e., SQL API, MongoDB API, and Cassandra API
True/False: Enabling CORS can prevent SQL Injection.
- True
- False
Answer: False
Explanation: CORS does not prevent SQL Injection. CORS is about allowing different domains to interact, whereas SQL Injection is a code injection technique.
Under which circumstances does Microsoft recommend to use wildcard (*) in allowed origins?
- A. When resources are public and can be accessed by any domain
- B. When resources are private and specific to a domain
- C. When resources are shared among few domains
- D. Never
Answer: A. When resources are public and can be accessed by any domain
Explanation: The use of wildcard (*) is only recommended when the resources are public and can be accessed by any domain. Otherwise, it is advisable to list specific domains to maintain security.
Interview Questions
What is Cross-Origin Resource Sharing (CORS)?
Cross-Origin Resource Sharing (CORS) is a mechanism that uses additional HTTP headers to allow a user agent to gain permission to access selected resources from a server on a different origin/domain than the site currently in use.
How does CORS improve web security in Azure Cosmos DB?
CORS adds an extra security layer by allowing only certain sites to request and receive your database information. It helps limit the potential for malicious attacks by specifying trusted origins.
How can you configure CORS settings in Azure Cosmos DB?
CORS settings can be configured in Azure Cosmos DB via the Azure portal, Azure CLI, PowerShell, or the Azure SDKs.
What details are required when configuring CORS rules in Azure Cosmos DB?
When configuring CORS rules, you need to specify the origins that are allowed to make cross-origin calls and the HTTP methods (GET, POST, DELETE, etc.) that they can use.
What does the “*” wildcard mean in Azure Cosmos DB’s CORS settings?
The “*” wildcard can be used in Azure Cosmos DB’s CORS settings to allow all origins. It should be used cautiously because it opens your Azure Cosmos DB to access from any location.
What happens if multiple CORS rules are configured in Azure Cosmos DB?
If you specify more than one rule, then an incoming request is valid if any rule allows it.
Can you configure CORS settings at the document level in Azure Cosmos DB?
No, CORS settings are set at the service level in Azure Cosmos DB, not at the individual document or collection level.
Can I use Azure CLI to set up CORS in Azure Cosmos DB?
Yes, Azure CLI commands can be used to configure CORS by using the ‘az cosmosdb update’ command along with the –allowed-origins flag.
Are the CORS settings in Azure Cosmos DB case sensitive?
No, the CORS settings in Azure Cosmos DB are not case sensitive.
How to delete an existing CORS rule in Azure Cosmos DB?
An existing CORS rule in Azure Cosmos DB can be deleted through the Azure portal, Azure CLI, PowerShell, or the Azure SDKs.
What repercussions could occur if CORS is not set up correctly in Azure Cosmos DB?
If CORS is not set up correctly, clients’ requests may be blocked, resulting in a potential loss of service for those users. It may also result in the exposure of sensitive data if the “*” wildcard is used incorrectly.
Is CORS configuration mandatory for every Azure Cosmos DB setup?
No, CORS configuration is not mandatory for every Azure Cosmos DB setup. It is dependent on your specific application’s requirements and security posture.
What is the meaning of the “cors.allowedOrigins” setting in Azure Cosmos DB configuration?
“cors.allowedOrigins” is a setting where you specify the origin URLs that are permitted to make cross-origin requests to your Azure Cosmos DB.
Does enabling CORS impact the performance of Azure Cosmos DB?
Enabling CORS shouldn’t have a significant impact on the performance of Azure Cosmos DB as it’s mainly a mechanism to enable communication between different origins.
How many CORS rules can be defined in Azure Cosmos DB?
Azure Cosmos DB does not limit the number of CORS rules you can define. You can specify as many rules as your application requires.
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