Letter of Agency
A Letter of Agency (LOA) - sometimes referred to as a Letter of Authorization - is a document that authorizes Cloudflare to announce a prefix(es) on behalf of another entity. The LOA is required by Cloudflare's transit providers so they can accept the routes Cloudflare advertises on behalf of another entity.
The letter must contain both the prefixes you are authorizing Cloudflare to announce and which ASN they will be announced under. Cloudflare can announce a prefix under your ASN or you can use Cloudflare's ASN, which is AS13335.
Cloudflare accepts digital signatures on an LOA, as long as it is clear who is signing the LOA.
You can use the below template when creating an LOA document.