* perf: remove call client old- method via ?next=client
* feat: add 2 decorators for login-get and login-callback-get to set next_page and get next_page from session
* perf: code style
* perf: handling the next parameter propagation issue in third-party authentication flows
* perf: request.GET.dict() to copy()
* perf: style import
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Co-authored-by: Bai <baijiangjie@gmail.com>