Builds the string the envelope sender signature covers: mjdiag-sender-v1:${recipientKeyId}:${ephemeralPublicKeyBase64}:${manifestSha256}.
mjdiag-sender-v1:${recipientKeyId}:${ephemeralPublicKeyBase64}:${manifestSha256}
Optional
Builds the string the envelope sender signature covers:
mjdiag-sender-v1:${recipientKeyId}:${ephemeralPublicKeyBase64}:${manifestSha256}.