Overcoming cookie limitations: SSO SAML feature with cross-domain compatibility

In the domain of web development, implementing Single Sign-On (SSO) and Security Assertion Markup Language (SAML) features are crucial for smooth user experiences. However, developers often encounter challenges when working with cookie sizes and cross-domain limitations. In this article, we will explore a specific scenario where the cookie size exceeded the buffer limit and how it was resolved by adjusting the buffer size and addressing cross-domain issues within the same subdomain.

The Cookie Size Challenge:

While working on a project involving SSO SAML functionality, a significant challenge emerged when the response cookie size reached approximately 7kb. The server, which employed NGINX, had a buffersizelimit set to 4kb, resulting in an issue where the response cookie exceeded the server's capacity.

Solution: Increasing the Buffer Size Limit

We decided to increase the buffersizelimit from 4kb to 16kb. This adjustment allowed the server to handle larger response cookies without triggering any buffer overflow errors. By increasing the buffer size limit, the server became capable of accommodating the 7kb response cookie comfortably.

Addressing Browser Limitations:

It was essential to consider the limitations imposed by web browsers. Most browsers only support cookies up to 4kb in size. To avoid this restriction, we adopted a clever approach: splitting the cookie into smaller parts while ensuring the cookie size remained below the browser's limit.

We divided the response cookie into multiple chunks, each containing approximately 3,000 words. By splitting the cookie in this manner, we ensured that each individual chunk was below the 4kb threshold. This strategy allowed us to send multiple smaller cookies to the browser while keeping each cookie size below the browser's maximum limit.

Combining Cookies on the Frontend:

Once the cookie was split into smaller segments, the next challenge was to reassemble them on the frontend. We created a mechanism to receive the cookie chunks separately and then combined them into a single cookie within the browser. By utilizing JavaScript and the Document Object Model (DOM), we were able to manage the individual cookie parts and reconstruct the original cookie.

Resolving Cross-Domain Cookie Issues:

Another challenge that often arises when working with cookies is the cross-domain limitation. Browsers typically prevent cookies from being shared across different domains for security reasons. However, in this scenario, the SSO SAML feature required the cookie to be accessible across subdomains within the same main domain.

To overcome this limitation, we ensured that the SSO SAML cookie was explicitly set to the main domain and utilized a wildcard for the subdomain. For example, instead of setting the cookie to "example.com," we set it to ".example.com." This approach made the cookie accessible to all subdomains of the main domain, effectively resolving the cross-domain cookie problem.

Working with SSO SAML features often presents challenges related to cookie sizes and cross-domain limitations. By increasing the buffersizelimit in the NGINX server, we successfully addressed the issue of a response cookie exceeding the buffer limit. Furthermore, by splitting the cookie into smaller chunks and reassembling them on the frontend, we overcame browser limitations. Lastly, by setting the cookie to the main domain with a wildcard for subdomains, we resolved the cross-domain cookie problem. These solutions ensured the seamless functioning of the SSO SAML feature, ultimately providing users with a smooth and secure experience.

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