How to generate a random Vector3 point inside a polygon

Question

I work on Unity3D and I have a Vector3 array, this array is the vertex of a polygon. Now I try to Generate a random point inside the polygon and I don't know how many vertex I have.

e.g:

polygonBorders = new Vector3[3];

        polygonBorders[0] = new Vector3(35.3f, 1.3f, -20.1f);
        polygonBorders[1] = new Vector3(35.3f, 1.3f, -3.42f);
        polygonBorders[2] = new Vector3(52.11f, 1.3f, -3.42f);

this is my polygon and I want a method like that:

 Vector3 GeneratePointInsidePolygon(Vector3[] polyogn, Vector3 point)

I try to find a solution all over the Internet and there is no solution or libraey