WebhookPolicyJwtAlg
One of:
- 
none: No digital signature or MAC performed - 
hs256: HMAC using SHA-256 - 
hs384: HMAC using SHA-384 - 
hs512: HMAC using SHA-512 - 
rs256: RSA using SHA-256 - 
rs384: RSA using SHA-384 - 
rs512: RSA using SHA-512 - 
es256: ECDSA using P-256 and SHA-256 - 
es384: ECDSA using P-384 and SHA-384 - 
es512: ECDSA using P-521 and SHA-512