FEATURE/MEDIUM: userList: generate random secure password

[amelhusic]

This change previously hard coded password ("insecure-password" in HAProxy config) usage and instead use hashed password("password").
So, on every start up a random password is generated, hashed and then saved to HAProxy conf.
Generated password is stored in memory, while hashed password is saved to HAProxy conf.

[amelhusic]

This is related to #12

[ShimmerGlass]

This should use crypto/rand instead of math/rand. math/rand is not a secure random source.

[amelhusic]

I applied suggested changes.

[ShimmerGlass]

I don't think hashing the password is needed here. b64 should only output chars compatible with the config file format and hashing doesn't add entropy to the generated string.
Otherwise LGTM.

[amelhusic]

If we remove hashing func, then we need to use insecure-password again. From the issue #12:

One possible simple solution would be to generate a strong crypto-random password for HAProxy on every startup so it's only in-memory in the consul-haproxy process and passed through to HAProxy. I guess the Config is written to disk so I'd suggest using the secure (hashed) password config to pass it through and hashing the random password in consul-haproxy. That way you can have high confidence that the only process able to configure the proxy is same consul-haproxy process that stated it.

My understanding from above is that generated password should be in memory and encrypted password saved to disk. What do you think?

EDIT: After rethinking this, I think also we don't need a password. Also, usage of password will affect a CPU usage according to docs. So, I removed hashing func.

[ShimmerGlass]

LGTM