Seems like the accepted answer does not work anymore. I found the correct method from another post: https://stackoverflow.com/a/46811403/6368026
Now you should use:
http://www.youtube.com/embed/videoseries?list=USERID And the USERID is your youtube user id with 'UU' appended.
For example, if your user id is TlQ5niAIDsLdEHpQKQsupg then you should put UUTlQ5niAIDsLdEHpQKQsupg. If you only have the channel id (which you can find in your channel URL) then just replace the first two characters (UC) with UU.
So in the end you would have an URL like this:
http://www.youtube.com/embed/videoseries?list=UUTlQ5niAIDsLdEHpQKQsupg