Code required a tempered (safety) glass at most entries. Your door requires a custom size. If the broken glass crumbled to small bits rather than shards, the glass was tempered and should be replaced with same. My experience is that it is fastest to simply call a glazier for this, partiuclarly if you are not familiar with how glass is mounted in this panel. If you can figure how how glass is mounted, you can order glass pre-cut (safety or standard) and install it yourself. If you DIY you may save up to $50-$80 in labor costs, but it will take you longer assuming you can even find the materials.