Populate with earthaccess.login guide in User Guide Authentications docs

CHANGELOG.md

@@ -36,6 +36,7 @@ and this project uses [Semantic Versioning](https://semver.org/spec/v2.0.0.html)
 - Auto-add comment to PR that requires maintainer to review and re-run
   integration tests ([#824](https://github.com/nsidc/earthaccess/issues/824))
   ([@chuckwondo](https://github.com/chuckwondo))
+- Add authentication to User Guide documentation. ([#763](https://github.com/nsidc/earthaccess/pull/763)) ([@andypbarrett](https://github.com/andypbarrett))
 
 ### Removed
 

docs/user_guide/authenticate.md

@@ -1,11 +1,157 @@
 # Authentication
 
-Introduces the `earthaccess.login` method for managing Earthdata Login and cloud credentials.
+You can use `earthaccess` to search for datasets and data without needing to log in.
+However, to access (download or stream) NASA Earth science data, whether from one of the NASA
+Distributed Active Archive Centers (DAACs) or from NASA Earthdata Cloud, you need
+an Earthdata Login account.  You can register for a free Earthdata Login (EDL) account [here](https://urs.earthdata.nasa.gov/).  
 
-!!! note "This Page is a Work in Progress"
+Once you have an Earthdata Login account, you may use the `earthaccess.login` method to manage Earthdata Login credentials and, when you are working with cloud-hosted data, cloud credentials.
 
-    We are reorganizing and updating the documentation, so not all pages are complete.  If you are looking for information about authenticating using earthaccess see the
-    How-Tos and Tutorials in links below.
+`earthaccess.login` offers three methods of logging in (or authenticating) using EDL:
 
-    * [Quick start](../quick-start.md)
-    * [How-To Authenticate with earthaccess](../howto/authenticate.md)
+* [a manual login method](#login-manually), where you enter EDL username and password manually
+* an automatic login method using EDL credentials stored in a [`.netrc`](#login-using-a-netrc) file
+* an automatic login method using EDL credentials stored in [environment variables](#login-using-environment-variables).
+
+By default, `earthaccess.login()` will look for a `.netrc` or environment variables first.  If neither of these are found, it will prompt you to enter your username and password.  The three methods are described in detail below.  
+
+`earthaccess.login` can also be used to login to [different endpoints](#accessing-different-endpoints) and [get S3 credentials](#using-earthaccess-to-get-credentials).
+
+## Login Manually
+
+If you have not created a `.netrc` file or `EARTHDATA_USERNAME` and `EARTHDATA_PASSWORD` environment variables, you can use the following approach to login.
+
+```
+>>> import earthaccess
+
+>>> auth = earthaccess.login()
+Enter your Earthdata Login username: your_username
+Enter your Earthdata password: 
+```
+
+You don't need to assign the result of `earthaccess.login()` to a variable but doing so enables access session information.  These are discussed in [Accessing Session Information]().
+
+Setting `strategy=interactive` will force a manual login.
+
+## Login using a `.netrc`
+
+!!! warning "Do not use this strategy on untrusted machines or with shared accounts" 
+
+    `earthaccess` does not currently support encrypted `.netrc` files.   This strategy of writing credentials in plain text to disk
+    should not be used on untrusted machines or shared user accounts.
+
+
+### Creating a `.netrc` file
+
+#### Using `earthaccess.login` to create a `.netrc` file
+
+You can use `earthaccess.login` to create a `.netrc` for you.
+```
+earthaccess.login(persist=True)
+```
+You will then be prompted for your Earthdata Login username and password.  A `.netrc` (or `_netrc`) file will be created automatically.
+
+#### Manually creating a `.netrc` file for Earthdata Login Credentials
+
+=== "MacOS"
+    Type the following on your command line, replacing `<username>` and `<password>` with your
+    Earthdata Login credentials.
+
+    ```
+    echo "machine urs.earthdata.nasa.gov login <username> password <password>" >> $HOME/.netrc
+    chmod 600 $HOME/.netrc
+    ```
+
+=== "Linux"
+    Type the following on your command line, replacing `<username>` and `<password>` with your
+    Earthdata Login credentials.
+
+    ```
+    echo "machine urs.earthdata.nasa.gov login <username> password <password>" >> $HOME/.netrc
+    chmod 600 $HOME/.netrc
+    ```
+
+=== "Windows"
+    In a `CMD` session, create a `%HOME%` environment variable.  The following line
+    creates `%HOME%` from the path in `%USERPROFILE%`, which looks something like
+    `C:\Users\"username"`.
+    ```
+    setx HOME %USERPROFILE%
+    ```
+    You now need to create a `_netrc` file in `%HOME%`.
+    ```
+    echo "machine urs.earthdata.nasa.gov login <username> password <password>" >> %HOME%\_netrc
+    ```
+
+## Login using environment variables
+
+Alternatively, Earthdata Login credentials can be created as environment variables `EARTHDATA_USERNAME` and `EARTHDATA_PASSWORD`.
+
+=== "MacOS"
+    If you want to set the environment variables for the current shell session, type the following on the command line.
+    ```
+    export EARTHDATA_USERNAME="username"
+    export EARTHDATA_PASSWORD="password"
+    ```
+    If you want to set these environmental variables permanently, add these two lines to the appropriate configuration files for your operating system.
+
+
+=== "Linux"
+    If you want to set the environment variables for the current shell session, type the following on the command line.
+    ```
+    export EARTHDATA_USERNAME="username"
+    export EARTHDATA_PASSWORD="password"
+    ```
+    If you use `bash` and would like to set these environmental variables permanently, add these two lines to your `~/.profile` file:
+    ```
+    EARTHDATA_USERNAME="username"
+    EARTHDATA_PASSWORD="password"
+    ```
+    For other shells, use the recommended method to persistently set these environment variables for whichever shell you use.
+
+=== "Windows"
+    To set the environment variables for the current `CMD` session, type the following:
+    ```
+    setx EARTHDATA_USERNAME "username"
+    setx EARTHDATA_PASSWORD "password"
+    ```
+    To set these environmental variables permanantly  
+    1. Open the start menu.  
+    2. Search for the "Advanced System Settings" control panel and click on it.  
+    3. Click on the "Environment Variables" button toward the bottom of the screen.  
+    4. Follow the prompts to add the variable to the user table.  
+
+
+## Accessing different endpoints
+
+### Earthdata User Acceptance Testing (UAT) endpoint
+
+If your EDL account is authorized to access the User Acceptance Testing (UAT) system,
+you can set earthaccess to work with its EDL and CMR endpoints
+by setting the `system` argument at login, as follows:
+
+```python
+import earthaccess
+
+earthaccess.login(system=earthaccess.UAT)
+
+```
+
+## Using `earthaccess` to get S3 credentials
+
+`earthaccess.login` is a very convenient way to manage and provide Earthdata Login credentials.  `earthaccess.login` can also be used to obtain S3 credentials to access NASA Earthdata Cloud.  If you use `earthaccess` to access data in the cloud, you do not have to use this option, `earthaccess` handles this.  However, if you are using other packages, such as `h5coro`, `earthaccess` can save a lot of time.
+
+```
+import earthaccess
+import xarray as xr
+import h5coro
+
+auth = earthaccess.login()
+s3_credentials = auth.get_s3_credentials(daac="NSIDC")
+
+s3url_atl23 = 'nsidc-cumulus-prod-protected/ATLAS/ATL23/001/2023/03/' \
+                '01/ATL23_20230401000000_10761801_001_01.h5'
+ds = xr.open_dataset(s3url_atl23, engine='h5coro', 
+                     group='/mid_latitude/beam_1', 
+                     credentials=s3_credentials)
+```