[DOCS] Port over "How to configure credentials using YAML or env vars…

…" from RTD to Docusaurus

docs/guides/setup/configuring-data-contexts/how-to-configure-credentials-using-a-yaml-file-or-environment-variables.md

@@ -1,5 +1,101 @@
 ---
 title: How to configure credentials using a YAML file or environment variables
 ---
+import Prerequisites from '../../connecting_to_your_data/components/prerequisites.jsx'
 
-This article is a stub.
+This guide will explain how to use a YAML file and/or environment variables to populate credentials (or any value) in your ``great_expectations.yml`` project config.
+
+<Prerequisites>
+
+  - [Set up a working deployment of Great Expectations](../../../tutorials/getting-started/intro.md)
+
+</Prerequisites>
+
+
+Steps
+------
+
+1. Decide where you would like to save the desired credentials or config values - in a YAML file, environment variables, or a combination - then save the values. In most cases, we suggest using a config variables YAML file. YAML files make variables more visible, easily editable, and allow for modularization (e.g. one file for dev, another for prod).
+
+  :::note
+
+    - In the ``great_expectations.yml`` config file, environment variables take precedence over variables defined in a config variables YAML
+    - Environment variable substitution is supported in both the ``great_expectations.yml`` and config variables ``config_variables.yml`` config file.
+
+  :::
+
+  If using a YAML file, save desired credentials or config values to ``great_expectations/uncommitted/config_variables.yml`` or another YAML file of your choosing:
+
+  ```yaml
+  # great_expectations/uncommitted/config_variables.yml
+
+  my_postgres_db_yaml_creds:
+    drivername: postgres
+    host: 127.0.0.778
+    port: '7987'
+    username: administrator
+    password: ${MY_DB_PW}
+    database: postgres
+  ```
+
+  :::note
+
+    - If you wish to store values that include the dollar sign character ``$``, please escape them using a backslash ``\`` so substitution is not attempted. For example in the above example for postgres credentials you could set ``password: pa\$sword`` if your password is ``pa$sword``. Say that 5 times fast, and also please choose a more secure password!
+    - When you save values via the CLI, they are automatically escaped if they contain the ``$`` character.
+    - You can also have multiple substitutions for the same item, e.g. ``database_string: ${USER}:${PASSWORD}@${HOST}:${PORT}/${DATABASE}``
+
+  :::
+
+  If using environment variables, set values by entering ``export ENV_VAR_NAME=env_var_value`` in the terminal or adding the commands to your ``~/.bashrc`` file:
+
+  ```bash
+  export POSTGRES_DRIVERNAME=postgres
+  export POSTGRES_HOST=localhost
+  export POSTGRES_PORT='5432'
+  export POSTGRES_USERNAME=postgres
+  export POSTGRES_PW=''
+  export POSTGRES_DB=postgres
+  export MY_DB_PW=password
+  ```
+
+2. If using a YAML file, set the ``config_variables_file_path`` key in your ``great_expectations.yml`` or leave the default.
+
+  ```yaml
+  # great_expectations/great_expectations.yml
+
+  config_variables_file_path: uncommitted/config_variables.yml
+  ```
+
+3. Replace credentials or other values in your ``great_expectations.yml`` with ``${}``-wrapped variable names (i.e. ``${ENVIRONMENT_VARIABLE}`` or ``${YAML_KEY}``).
+
+  ```yaml
+  # great_expectations/great_expectations.yml
+
+  datasources:
+    my_postgres_db:
+      class_name: SqlAlchemyDatasource
+      data_asset_type:
+        class_name: SqlAlchemyDataset
+        module_name: great_expectations.dataset
+      module_name: great_expectations.datasource
+      credentials: ${my_postgres_db_yaml_creds}
+    my_other_postgres_db:
+      class_name: SqlAlchemyDatasource
+      data_asset_type:
+        class_name: SqlAlchemyDataset
+        module_name: great_expectations.dataset
+      module_name: great_expectations.datasource
+      credentials:
+        drivername: ${POSTGRES_DRIVERNAME}
+        host: ${POSTGRES_HOST}
+        port: ${POSTGRES_PORT}
+        username: ${POSTGRES_USERNAME}
+        password: ${POSTGRES_PW}
+        database: ${POSTGRES_DB}
+  ```
+
+
+Additional Notes
+--------------------
+
+- The default ``config_variables.yml`` file located at ``great_expectations/uncommitted/config_variables.yml`` applies to deployments created using ``great_expectations init``.