How accurate do you need the lines to be? Try something like this to begin with:
var start = {lat:90.40237426757811, lng:23.75015391301012}
var end = {lat:88.34930419921875, lng:22.573438264572406}
var n = 100; // the number of coordinates you want
coordinates = []
for(var i = n - 1; i > 0; i--){
coordinates.push( {lat: start.lat*i/n + end.lat*(n-i)/n,
lng: start.lng*i/n + end.lng*(n-i)/n});
}
This isn't accurate because the world isn't flat and over long distances it will begin to look wrong.
The full maths of plotting straight lines on projected globes is more difficult but there's a great explanation here: http://www.movable-type.co.uk/scripts/latlong.html Not far down the page there's a formula to calculate the midpoint of two given points.
Use that formula, then use the midpoint you've found with each end point to find two more points then use those points and so on until you have enough for a smooth line.