[fullstackchris]

This is incorrect. Almost all brokers nowadays allow for OAuth connections where you can stream any data you'd see in your broker platform to any consuming web application (given the consuming web application does all the paperwork, dev work, and so on)

[throwaway2037]

    > Almost all brokers

That is a mighty broad brush. I can confidently say that this is untrue for many brokers in continental Europe and North Asia. US brokers? If yes, can you provide some examples?

[immibis]

(with a contractual obligation to never share the data with anyone else or they'll sue you for all you're worth)