Client Secret with Backslash

[Wingard, Nathaniel (Chapin)]

I've been trying to set a client secret with a trailing backslash and find myself confused by the results. I am running the Debian 9 provided freeradius 3.0.12 (freeradius-3.0.12+dfsg-5+deb9u1).

Secret I want:
asdf\

Attempts (failures):
secret = asdf\
 - Results in config parsing error
secret = asdf\\
 - Results in config parsing error
secret = 'asdf\'
 - Results in config parsing error
secret = "asdf\"
 - Results in config parsing error
secret = 'asdf\\'
 - Results: asdf\\
secret = "asdf\\"
 - Results: asdf\\

Attempts (successes?)
secret = "as\df"
 - Results: as\df
secret = "as\\df"
 - Results: as\\df

I expected the last of my failures to work per https://networkradius.com/doc/3.0.10/unlang/data_single.html but it seems only \' is treated as an escape sequence in the client secret. Is there any way to have a client secret with a trailing backslash, and as an extension, can I have the string literal \' in my secret?

Thanks,
Nathaniel