Create functions to log into DATIM

[jacksonsj]

No description provided.

[sam-bao]

@jason-p-pickering @jacksonsj Should we be making us of the keyring for login passwords in some way?

https://cran.r-project.org/web/packages/keyring/keyring.pdf

[sam-bao]

@jason-p-pickering recording details from our slack conversation here:

Logins functions should

1. Accept a config file with no slash, a slash, or multiple slashes for baseurl and mutate this to a single trailing slash
2. All other API calls in code, should never start with a slash
3. A utility function to a) encode all URIs and b) check if there are any double slashes (which we know will fail)

• e.g. a wrapper around utils::urlencode that thrown an error if there is a "//" other than in "https://"