# Authentication

Unfortunately, the authentication process is rather complex in the Copernicus Data Space Ecosystem (CDSE). Different services require different authentication schemes. This vignette attempts to address all relevant authentication methods, and which is needed where. And which steps you need to complete to obtain the required secrets.

## Authentication methods

In essence there are three authentication methods used in this package for the CDSE:

- Access Token; it needs:
  - Client ID
  - Client Secret
- Public Access Token; it needs:
  - User identifier
  - User password
- S3 key + secret

Both access tokens are long pieces of encrypted codes that you can request with specific secrets that are associated with your CDSE account. Both access tokens are only valid for a short period of time (usually about 10 minutes), so you may need to obtain a fresh token once in a while.

## What and Where?

The list below shows which of the three authentication methods is required by which functions in this package:

- Access Token; required by:
  - `dse_get_token_details()` For decoding the token
  - Account info
    - `dse_usage()`
  - SentinelHub functions:
    - `dse_sh_features()`
    - `dse_sh_process()`
    - `dse_sh_search_request()`
    - `dse_sh_use_requests_builder()`
    - `dse_sh_features()`
- Public Access Token; required by:
  - `dse_set_gdal_token()` For making the token visible to the GDAL driver
  - `dse_get_token_details()` For decoding the token
  - `dse_odata_download_path()`
  - `dse_stac_download()` in case of a https download
  - Account info
    - `dse_user_statistics()`
- S3 key + secret; required by:
  - `dse_stac_download()` in case of an S3 download
  - `dse_odata_download()`
  - `dse_s3_download()`

## Setting up Authentication Methods

### A CDSE Account

All authentication methods share a commonality: They all require a CDSE user account. You can create one by visiting the login page and click “register”. Fill out the form and follow the instructions.

### A Public Access Token

After completing this registration you will have a user id (usually your e-mail) and a password (created by yourself). You can use those to obtain a public access token, which you can use for the functions listed above. You can obtain such a token by calling `dse_public_access_token()`, with your user Id and password.

### A Non-Public Access Token

Getting a (non-public) access token, you need to complete additional steps. In order to retrieve such a key, you need to register a client. To register such a client, visit the Sentinel Dashboard and go to “User settings”. There you will have the option to create an OAuth client. Follow the instructions, and make sure to safely copy the client id and secret. The latter is only displayed once. More detailed instructions are provided by the API documentation

You can now retrieve an access token (required by the functions listed above) by calling `dse_access_token()` with the client Id and client secret that you have created with the steps above.

### S3 Key and Secret

To create an S3 key and secret, you should visit the s3-credentials page, and log in with your CDSE account details. By clicking “add credential”, you can create a new key and secret. Store them in a safe place, as the secret is only shown once. You can pass the key and secret as `s3_key` and `s3_secret` arguments to functions requesting them (see above).

## Masking Secrets

As you might want to share your R scripts that use the CopernicusDataspace package, but don’t want to share personal secret information, there is a way around including them in your script.

You can store them as system environment variables, which are automatically detected by this package.

You can set them with `Sys.setenv()` at the start of each R session. You can also edit your `.renviron`, such that they are loaded automatically each new R session. The easiest way to do this is by calling `usethis::edit_r_environ()` and add the following lines.

    CDSE_API_USERNAME="<your_CDSE_username>"
    CDSE_API_PASSWORD="<your_CDSE_password>"
    CDSE_API_CLIENTID="<your_client_id>"
    CDSE_API_CLIENTSECRET="<your_client_secret>"
    CDSE_API_S3ID="<your_s3_key>"
    CDSE_API_S3SECRET="<your_s3_secret>"

Obviously, you need to replace the text between `<>` with your personal details. In a new R session, these environment variables are available, and you no longer have to pass secret information as arguments to the functions. They are obtained from the environment.

## Memoise

It is important to note that the functions `dse_access_token()` and `dse_public_access_token()` are both wrapped in `memoise::memoise()`. This means that the function result is stored in memory and when the function is called again, previous results are reused.

One advantage is that it speeds up operations, when you have multiple sequential calls that need access tokens. It will also prevent rate limiting actions, where the server might block you when you excessively request tokens.

A disadvantage is that you token might expire, and an old token is reused due to the memoise strategy. If this happens, you can wipe the memoised token by calling `memoise::forget(dse_access_token)` or `memoise::forget(dse_public_access_token)`, respectively. After that you will get a fresh token when calling the token functions.