There are a number of ways to specify a password, each represented by
a separate setting. Newsboat looks for settings in certain order, and uses the
first one that it finds. The exact order is described below.

Settings are prefixed by API names; e.g. `newsblur-password`,
`feedhq-passwordeval`. All APIs support all the settings, so examples below use
`REMOTEAPI` for prefix. Replace it with the name of the remote API you use.

The first setting Newsboat checks is `REMOTEAPI-password`. It should contain the
password in plain text.

The second setting Newsboat checks is `REMOTEAPI-passwordfile`. It should
contain a path to a file; the first line of that file should contain the
password in plain text. If the file doesn't exit, is unreadable, or its first
line is empty, Newsboat will exit with an error.

The third setting Newsboat checks is `REMOTEAPI-passwordeval`. It should
contain a command that, when executed, will print out the password to stdout.
stderr will be passed through to the terminal.

If the first line of command's output is empty, or the command fails to
execute, Newsboat will exit with an error. This is the most versatile of all
the options, because it lets you emulate every other and more; let's look at it
in more detail.

For example, a user might want to store their password in a file encrypted by
GPG. They create the file like that:

    $ gpg --encrypt --default-recipient-self --output ~/.newsboat/password.gpg

They enter their password, press Enter, and finish the command by pressing ^D
(Control and d simultaneously). Then, they specify in their Newsboat config:

    REMOTEAPI-passwordeval "gpg --decrypt ~/.newsboat/password.gpg"

Now every time they start Newsboat, GPG will be ran. It'll probably ask for
keyring password, then decrypt the file, and pass its contents to Newsboat,
which will use it to authenticate with the remote API.

Note that Newsboat will keep the password in memory the entire time Newsboat is
running. Other programs might be able to dump the memory and obtain the
password. We don't currently have any protection from that; patches are
welcome.

The user might use any other command here; for example, they could fetch the
password from GNOME keyring, KeePass, or somewhere else entirely. The
possibilities are truly endless.

If no of the aforementioned settings were found, Newsboat will ask the user for
the password using an interactive prompt. If the password that the user enters
is empty, Newsboat will give up and exit with an error.
