Security with authentication tokens

Greetings,

Thanks for putting this together! We do now have a signing library for go but it's fine to have more than one.

However, in order to use this as an akamai signing library, you need to change how you're dealing with the credentials. Putting them in the environment is very insecure and it's important to protect those pieces of information. The other signing libraries (and any signing library for Akamai) use a ~/.edgerc file which can be locked down with permissions.

The format of this file is as follows:
[default]
client_secret = xxx=
host = akab-xxx/
access_token = xxx
client_token = xxx
max-body = 131072

The section name is used by the signing libraries to know which of the sections to use for the credentials. Please implement this for the signing library. This is done in the other go repository which will be released shortly.

Thanks,
Kirsten

Start by locating how the signing library currently reads credentials from the environment. Compare that behavior with the requested ~/.edgerc format, including named sections and the listed credential fields. Done means the library can use a selected section from ~/.edgerc while protecting the credential data as described.

Written by the indexing model from the issue text.