Retrieves the OMOPHub API key from multiple sources in priority order:
Explicit argument
OMOPHUB_API_KEYenvironment variableSystem keyring (if
keyringpackage is installed)
Examples
if (FALSE) { # \dontrun{
# From environment variable
Sys.setenv(OMOPHUB_API_KEY = "your_api_key")
key <- get_api_key()
# Explicit key
key <- get_api_key("your_api_key")
} # }