Prepositions – How to Welcome Someone Who Returned to Their Home Country

With is correct:

I'd like to confirm with you that you will finish the report by Thursday.

You can also request confirmation:

Please confirm that you'll finish the report by then.
I need your confirmation that you'll do it on time.

With this sense, you can also confirm something for someone:

Let me look at my calendar to confirm that for you.

That is, to act on their request for confirmation.

When you say developed by someone, it means that the product or thing was developed by that someone- the developer of the product. When you say developed by ABC, inc. it means that the product or thing was developed by ABC's staff- the employees collectively working on the product.

When you say, developed at ABC, inc. it means that the product was developed at ABC, indicating a location of the company in question.

In most cases it would roughly give the same meaning, as most products are developed both by a company and at a company. However, it's possible that the product is developed or designed by a company but assembled at a different place and by different people. For example:

The iPhone was designed by Apple in California, but it was assembled by a different company in China.