Intresting

We have a web application [say for example WebA], which our firm uses to enter the transaction of our customers.
We also make use another web application [say for example WebB], owned by another firm, using the login provided by them to do some transactions . At end of the transaction(save the transaction), we manually input the transactions that we made in this[WebB] application back to our web application[WebA]
Now we want to automate this process.
So my questions are
  How to capture the data of "WebB" inside our web application "WebA"