 Quadratic Gauss sum

For $\omega =e^{2\pi i/p}$ and the Legendre symbol $\chi$, the quadratic Gauss sum isIt equals $\sqrt{p}$ for $p\equiv 1(\mathrm{mod}4)$ and $i\sqrt{p}$ for $p\equiv 3(\mathrm{mod}4)$ with the standard choice of square root.