Safer Nginx Basic Auth

#!/bin/bash

## read the thread that inspired this.
## https://security.stackexchange.com/questions/46883/is-every-hash-format-that-nginx-accepts-for-http-basic-auth-weak-against-brute-f

if [ $# != 3 ]; then
    echo -e "\nusage: ${0##*/} username password file\n"
    exit 1
fi

USERNAME="$1"
PASSWORD="$2"
AUTHFILE="$3"

SALT="$(openssl rand 30)"
SHA1="$(printf "%s%s" "$PASSWORD" "$SALT" | openssl dgst -binary -sha1)"

if [ -s "$AUTHFILE" ]; then
    read -r -p "\nThe file \"$AUTHFILE\" exists, do you want to overwrite it (yes, no, append)? [y/n/a] " response
    case "$response" in
        [Yy])
            printf "$USERNAME:{SSHA}%s\n" "$(printf "%s%s" "$SHA1" "$SALT" | base64)" > "$AUTHFILE";
            echo -e "\nOverwriting the existing file\n";
            exit 0;;
        [Aa])
            printf "$USERNAME:{SSHA}%s\n" "$(printf "%s%s" "$SHA1" "$SALT" | base64)" >> "$AUTHFILE";
            echo -e "\nAppending to existing file\n";
            exit 0;;
        [Nn])
            echo "\nExiting without saving\n";
            exit 0;;
        *)
            echo "\nThe provided answer is not valid. use either: 'Y' 'y' 'N' 'n' 'A' 'a'\n";
            exit 2;;
    esac
else
    printf "$USERNAME:{SSHA}%s\n" "$(printf "%s%s" "$SHA1" "$SALT" | base64)" > "$AUTHFILE";
    echo -e "\nWriting to file '$AUTHFILE'\n";
    exit 0
fi