Security is the most important aspect for any web application which contains sensitive data and information. For Example, Income Analyzer product development which deal with income documents like Form no 16 and other IRS forms. The best approach here is utilize that our web application should receive request only from specific clients whom we are trusting.
The best solution here would be using SSL 3.0 feature namely authenticates the client identity. The more details about the same is available here on the blow mention URL.