How can I have my bot start in a different dialog depending on user

Question

Basically, I want to have my bot on different pages using iframes and Bot Framework Web Chat.

Depending on what page the user opens the bot, a different dialog is called

Answer 1

Take a look at the backchannel. In your scenario you can pass a parameter from the Javascript via the back channel to set some value in UserData. Now your parameter will exist in state (in this case the IDataBag UserData) when your user first hits the bot.

Here is a C# sample of a 2-way backchannel

another C# sample using a 1 way backchannel