Hopf-Galois module structure of degree p extensions of p-adic fields

Let $p$ be an odd prime number. For a degree $p$ extension of $p$-adic fields $L\mathrm{/}K$, we give a complete characterization of the condition for the ring of integers ${\mathcal{O}}_L$ to be free as a module over its associated order in the unique Hopf-Galois structure on $L\mathrm{/}K$.