How do I compute the Green function of a differential operator?

[Kostas Koudas]

In Mathematica, you write:

GreenFunction[{-u''[x], u[0] == 0, u[1] == 0}, u[x], {x, 0, 1}, y]

and it gives you the Green function of the operator L=-d^2/dx^2 (the first argument, -u''[x]).

I want a corresponding function in SageMath.

Thanks in advance!