Move ssl-related params from TCPConnector to request args

[asvetlov]

Long story short

Now ssl configuration is tightly coupled with TCPConnector.

It is not convenient (user should create a connector and pass it into session) and disallows to use the same ClientSession for working with different ssl contexts etc.

I think we should move verify_ssl, fingerprint and ssl_context into ClientSession.request and ClientSession.ws_connect like we have done for proxy and proxy_auth (see #998).
Current TCPConnector's parameters should be kept as default values which may be overridden by request without any warning/error.

[magicgoose]

I think they should not be moved to single requests but to ClientSession instead. Multiple requests to the same host+port can reuse connection (or also not reuse, it's statically unknown in general) —

aiohttp/aiohttp/connector.py

Line 340 in 3da3a01

"""Get from pool or create new connection."""

and TLS params are inherently property of the connection, not a HTTP request, so if the user gives different TLS parameters to these requests, that would be very misleading and even non-stable behavior (because it's not known in general if the connection will be reused for a specific request).

@asvetlov do you agree?

[asvetlov]

I think if requests accepts verify and cert for every HTTP request call -- why aiohttp cannot do the same?

[magicgoose]

It can, of course, but I'm not sure if there are real advantages of doing this. But on second thought I see that it's probably fine for user, it would be just a little harder to implement. So, okay…

(at first I thought that there would be also things like which versions of TLS and which ciphers to negotiate with the server, and then there's no meaningful way of changing these constraints for next request with the same connection in general way, other than closing the connection and doing the handshake again, but if this level of control is not going to be allowed, then setting just verify and cert per request can be defined easily)

[asvetlov]

Fixed by #2184

[lock]

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