What are the two main approaches to obtain remote desktop connection passwords mentioned in the article?

The article describes two approaches: (1) Using a keylogger program to record the password as the user types it when mstsc.exe starts, and (2) reading the memory data of the mstsc.exe process to extract the password entered by the user. RdpThief implements the second approach, which is more stealthy and can capture credentials even if the user mistypes or enters them programmatically. For related techniques, see extracting credentials from lsass.exe and multi-user RDP.