There is a different way, without curl or other curl-like programs, without Python, Go, etc. It is smaller and faster, IME as a non-developer.

   post api.ctl.io/v2/authentication/login < 1.txt|openssl s_client -connect api.ctl.io:443 -ign_eof

post is a 702-character shell script. printf is a built-in.

      #!/bin/sh
      (  
      y=Connection;n=0;while read x;do
      x1=${1#*//};x2=${x1%%/*};x3=${x1#*/};
      x=$(printf "%s" "${x%%:*}:";echo "${x#*:}");
      if test x"${x3}" = x"${x2}";then x3="";fi;
      printf "%s\r\n%s\r\n%s\r\n%s\r\n" \
      "POST /${x3} HTTP/1.1" \
      "Host: ${x2}" \
      "Content-Type: application/json" \
      "Content-Length: ${#x}";
      if [ $n -gt 1 ];then
      printf "%s\r\n\r\n%s\r\n" "$y: keep-alive" "$x";else
      printf "%s\r\n\r\n%s\r\n" "$y: close" "$x";fi;
      export n=$((n+1));
      done;
      if [ $n -gt 1 ];then
      printf "%s\r\n%s\r\n%s\r\n" \
      "GET /robots.txt HTTP/1.0" \
      "Host: ${x2}" \
      "$y: close";fi;
      )

Data to be posted may be stored in a one-line file named "1.txt"

    cat > 1.txt
    { "username": "YOUR.USERNAME", "password": "YOUR.PASSWORD" }
    ^D

Examine the request

    post api.ctl.io/v2/authentication/login < 1.txt

POST the request

    post api.ctl.io/v2/authentication/login < 1.txt|nc -vvn 127.1 80

Alternatively, data to be posted can be read from stdin

    echo '{ "username": "YOUR.USERNAME", "password": "YOUR.PASSWORD" }' \
    |post api.ctl.io/v2/authentication/login \
    |nc -vvn 127.1 80

If the data to be posted is JSON formatted as multiple lines such as

    { 
      "username": "YOUR.USERNAME", 
      "password": "YOUR.PASSWORD" 
    }
    

then something like

    (tr -d '\12' < 1.txt;echo) \
    |post api.ctl.io/v2/authentication/login \
    |nc -vvn 127.1 80

For TLS we use proxy listening on 127.0.0.1, e.g., stunnel, sslsplit, haproxy, etc. This way we only ever have to type a single address and port, i.e., 127.1 80, or short alias for the hostname, e.g., echo 127.0.0.1 p >> /etc/hosts.

    cat > 1.cfg
    pid=/tmp/1.pid
    [ x ]
    accept=127.0.0.1:80
    client=yes
    connect=64.15.182.200:443
    options=NO_TICKET
    options=NO_RENEGOTIATION
    renegotiation=no
    sni=
    sslVersion=TLSv1.3
    ^D

    stunnel 1.cfg