[collectd] password check function

[Yves Mettier]

Hello,

I need to check a login/password that I store in a file.
I know how to use crypt (man crypt(3)), but I cannot use it :
- crypt is not reentrant (and I need a reentrant function)
- crypt_r is a GNU extension. May I use such a GNU extension in 
collectd ? I guess not, because of FreeBSD and other OS users.

I have searched in libgcrypt, but could not find a correct set of 
functions.

I need
- to check a login/password with a known login/crypted passwd
- to store it in a file in a human readable form (like in /etc/passwd, 
encoded with base64)
- to have more security than clear password or xor function
- compatibility with easy-to-use tools for users to fill the password 
file
- reentrant functions !!! (so crypt(3) won't fit)
- if possible, to have compatibility with what you can find in 
/etc/shadow on Linux (md5, sha256...)

What do you suggest ? Any hint ?

Regards,
Yves

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