secure signatures with vals

you'll need to make 2 new vals:

1. generate a keypair (keep this val private)

   Create val
   let vsExportedKeys = @easrng.generateKeys();

2. publish your public key (make this val public)

   Create val
   const vsPublicKey = () => @me.exportedKeys.publicKey;

call @easrng.valSign to get a signature.

Create val
const signature = await @easrng.valSign({ keys: @me.vsExportedKeys, data: {hello: "world"}})

the result will look something like this:

@easrng.htVgaVWWtvnz5AK0DnDaNON5gar5qJeaorfsTCiIr7ua_-D4HPmFrIrPMfwmCaMvI0CxKlYCUe9XTGm7r5s5C3siZGF0YSI6eyJoZWxsbyI6IndvcmxkIn0sInVzZXIiOiJlYXNybmciLCJleHByIjpudWxsfQ

you can also set an expiration date:

Create val
const signature = await @easrng.valSign({ keys: @me.vsExportedKeys, data: "this expires in 1 second", expireIn: 1000 })

call @easrng.valSignVerify to verify a signature

Create val
const { data, handle, expiresAt } = await @easrng.valSignVerify(signature)

with the example signature from earlier, data would be {hello: "world"}, handle would be easrng, and expiresAt would be null