Support arbitrary (optional) user-enterable data fields

[Klakurka]

Support arbitrary (optional) user-enterable data fields.

Example: https://donate.paybutton.org/

Show a new section before the QR code that has the new data entry form.

Using the following format, allow entering arbitrary fields:

fields='[{"name": "X", "text": "Y"}, {"name": "Z", "text": "A"}]' (maybe allow setting the "type" too for some basic validation? Eg. Text, email, checkbox, hidden.

These would appear in order from top to bottom, all optional. These values would be made available in the callback but could also be added directly into the DOM for convenience (to be discussed).

There would be a button at the bottom of the fields that has the same text as the text parameter for the button.

[Klakurka]

Things to think about for the future:

• Support for required fields.
• Support for different kinds of inputs (eg. drop down).

[Klakurka]

This is kinda related to doing it via BIP 21 (w/ the OP_RETURN extension) although a bit different.

If we detect a payment that doesn't match the QR code (like if a wallet doesn't support sending w/ OP_RETURN) then we can warn the user and take some kind of other action later.

[Klakurka]

I'm going to close this -- we can do this all via OP_RETURN to start, then BIP 70 later.

[Klakurka]

I've had a change of heart on this - let's do this "our way" initially and then later we can have BIP 70 be another option to get the same thing accomplished.

[Klakurka]

Allow configuring a set of inputs, more than just the 1 that we allow for op_return, that get set ahead of time on the server.

Use the payment id (provided by the server) to associate the data with the payment completion.

Have the data be entered before the QR code appears. Move the current op_return data entry option to this new "data entry" page/step.