Here is a list of all related documentation pages:

Structure of the source code
wpa_supplicant control interface
wpa_supplicant D-Bus API
Driver wrapper implementation (driver.h, drivers.c)
EAP peer implementation
EAP server implementation
hostapd control interface
Wi-Fi Direct - P2P module
Porting to different target boards and operating systems
Testing and development tools
Todo List
Deprecated List
Bug List