docs: Add example authentication configurations

Sources/swift-container-plugin/Documentation.docc/authentication.md

@@ -6,12 +6,101 @@ Configure the plugin to authenticate to your container registry.
 
 Many container registries require authentication in order to push images, or even pull them.
 The plugin reads your registry credentials from a `.netrc` file in your home directory.
-Add a record into the `.netrc` file for each registry you use, the plugin uses the authentication by the registry you choose.
+Add a record into the `.netrc` file for each registry you use.
+The plugin chooses the correct record based on the hostname of the registry's authentication server.
+
+> For some registries, such as Docker Hub [(see example)](<doc:#Docker-Hub>), the authentication server hostname might not be the same as the registry hostname you use when pushing and pulling images.
 
 The following example shows placeholder values for the registry `registry.example.com`:
 
 ```
 machine registry.example.com
   login myuser
   password mypassword
-```
+```
+
+The following examples show how to set up the plugin for some popular registry providers.
+
+### Docker Hub
+
+> Don't use your Docker Hub account password to push and pull images.
+> Create a Personal Access Token, which has restricted privileges, for each integration you use. 
+> By using separate tokens, you can monitor them independently and revoke one at any time.
+To create a `.netrc` entry for Docker Hub:
+
+1. Log into Docker Hub and [generate a Personal Access Token](https://docs.docker.com/security/for-developers/access-tokens/) for Swift Container Plugin.
+
+2. **Set the token's access permissions to *Read & Write*.**
+
+3. Copy the token and add it, together with your Docker ID, to your `.netrc` file under the machine name `auth.docker.io`:
+
+The final `.netrc` entry should be similar to this:
+
+```
+machine auth.docker.io
+  login mydockerid
+  password dckr_pat_B3FwrU...
+```
+
+### GitHub Container Registry
+
+> GitHub Container Registry only supports authentication using a [Personal Access Token (classic)](https://docs.github.com/en/packages/working-with-a-github-packages-registry/working-with-the-container-registry#authenticating-to-the-container-registry).
+> A fine-grained personal access token cannot be used.
+
+To create a `.netrc` entry for Github Container Registry:
+
+1. Log into GitHub and [generate a Personal Access Token (classic)](https://docs.github.com/en/authentication/keeping-your-account-and-data-secure/managing-your-personal-access-tokens#creating-a-personal-access-token-classic) for Swift Container Plugin.
+
+2. **Select the *write:packages* scope.**
+
+3. Copy the token and add it, together with your GitHub username, to your `.netrc` file:
+
+The final `.netrc` entry should be similar to this:
+
+```
+machine ghcr.io
+  login mygithubusername
+  password ghp_fAOsWl...
+```
+
+### Amazon Elastic Container Registry
+
+> Amazon Elastic Container Registry uses [short-lived authorization tokens](https://docs.aws.amazon.com/AmazonECR/latest/userguide/registry_auth.html#registry-auth-token) which expire after 12 hours.
+>
+> To generate an ECR authentication token, you must [first install the AWS CLI tools.](https://docs.aws.amazon.com/cli/latest/userguide/getting-started-install.html)
+
+To create a `.netrc` entry for Amazon Elastic Container Registry:
+
+1. Use the `aws` CLI tool to [generate an authentication token](https://docs.aws.amazon.com/AmazonECR/latest/userguide/registry_auth.html#registry-auth-token).
+You'll need to know the name of the [AWS region](https://docs.aws.amazon.com/global-infrastructure/latest/regions/aws-regions.html) in which your registry is hosted.
+Registries in different AWS regions are separate and require different authentication tokens.
+
+    For example, the following command generates a token for ECR in the `us-west-2` region:
+    ```
+    aws ecr get-login-password --region us-west-2
+    ```
+
+2. Copy the token and add it to your `.netrc` file.
+    * The format of the machine name is:
+
+        ```
+        <aws_account_id>.dkr.ecr.<region>.amazonaws.com
+        ```
+
+      You can [find your AWS account ID](https://docs.aws.amazon.com/accounts/latest/reference/manage-acct-identifiers.html) in the AWS Management Console or by running the following command:
+        ```
+        aws sts get-caller-identity \
+            --query Account \
+            --output text
+        ```
+    * **The login name must be `AWS`**.
+    * The token is a large encoded string.
+        It must appear in the `.netrc` file as a single line, with no breaks.
+
+The final `.netrc` entry should be similar to this:
+
+```
+machine 123456789012.dkr.ecr.us-west-2.amazonaws.com
+  login AWS
+  password eyJwYXlsb2FkIj...
+```