Fix code err code 401 when the password is empty in base_auth.

[CncGpp]

Fix: When setting the base_auth with a non-empty username and an empty password no auth is insert in the header.
The problem is similar to #650 but for the password.

[yhirose]

@CncGpp, thanks for the pull request, but it looks dangerous to accept blank password... RFC 7613 4.1 says:

A password MUST NOT be zero bytes in length. This rule is to be
enforced after any normalization and mapping of code points.

As you mentioned in #650, I made a change to allow username to be blank, since it looks a pretty common practice by popular servers. But I am not sure that the same thing can apply to password. Please give me more information why you really need it, or what servers are really allowing it. Thanks!

[CncGpp]

I'm using cpp-httplib to implement a basic client for ArangoDB (HTTP API), the DB password can be empty.

[yhirose]

@PixlRainbow, what do you think about this pull request?

[PixlRainbow]

I've looked into it; this should handle the case where a password needs to be sent that is blank. However, I found that certain servers may need the password field to be not present (not sent at all). But if your use case only requires the first case, then OK.

I would recommend however to use XOR instead of OR since we might not want to send basic auth header if both username and password are unset.

[yhirose]

@CncGpp, could you respond the comment from @PixlRainbow?

[CncGpp]

Sorry for the delay, wouldn't using XOR break the case where both userand pass are set? I think the OR is fine, when they are both empty it does not enter the if.

[PixlRainbow]

ahh my bad, I had mistaken the conditions backwards :D

[yhirose]

Thanks for the replies. I just merged it. Thanks for the contribution!