Calculate the content-digest of an HTTP request.

For all requests that contain a body, the content digest of the body must be calculated and added as a request header named content-digest, as described in the IETF draft for HTTP digest fields.

In summary, the digest calculation algorithm as used for the Investment API can be applied as follows:

• Capture the entire request body's byte stream.
• Calculate the SHA-512 hash of the body content.
• Encode the resulting value using Base64 encoding
• Add a request header named content-digest with this value: sha-512=:{digest value}:, where {digest value} is replaced by the result of the previous step.

From the above description you should now understand how to calculate a digest. Here are some examples you can use to check your understanding.