Note: I have already posted this on stackexchange, but have not yet gotten a response.
What are some good references for the Gauss composition law on binary quadratic forms in terms of Galois Cohomology?
I guess to be more general, I should ask for an exposition in terms of etale cohomology, but the etale cohomology is exactly the Galois cohomology in the number field case anyhow.
Thanks.