Add AWS account management docs and configurations

Directory accounts/aws/ contains docs and terraform configurations for
setting up a new AWS account, preparing it for use as the Flux test
infrastructure and managing the account further with all the
configurations in code.

Signed-off-by: Sunny <[email protected]>

.gitignore

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+.env
+.terraform
+.terraform.*
+terraform.tfstate*

accounts/aws/README.md

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+# AWS Account
+
+This documents how to set up an AWS account, prepare it to use for Flux test
+infrastructure and various usage workflows for managing the account.
+
+## New account initial setup
+
+- Once a new AWS account is created, log in as the root user and enable
+  multi-factor authentication for the root account, refer
+  https://docs.aws.amazon.com/IAM/latest/UserGuide/id_credentials_mfa_enable.html.
+- For Billing and Cost Management in the account, enable IAM access to billing,
+  refer https://docs.aws.amazon.com/IAM/latest/UserGuide/tutorial_billing.html.
+  This will enable the other users to be able to view the billing console if
+  they have the necessary permissions. With access to billing console, the users
+  would be able to know the cost of their resource usage and help keep the cost
+  in control.
+- For user management IAM Identity Center is used, which makes it easy to invite
+  and manage users in the account. AWS sends invitation email to the users and
+  provides an access portal to verify the email address, set up MFA device and
+  help log into the account easily. Choose a region, say `us-east-2`, switch to
+  the region in the AWS web console and enable IAM Identity Center, refer
+  https://docs.aws.amazon.com/SetUp/latest/UserGuide/setup-enableIdC.html. If
+  asked, create an AWS Organization and enable the Identity Center as an
+  organization, which is the recommended usage by AWS.
+  - After enabling IAM Identity Center, go to the IAM Identity Center console
+    settings and enable Multi-factor authentication, refer
+    https://docs.aws.amazon.com/singlesignon/latest/userguide/mfa-getting-started.html.
+    Configure the following options:
+      - Under **Prompt users for MFA**, select *Only when the sign-in context
+        changes*.
+      - Under **Users can authenticate with these MFA types**, select both
+        *Security keys* and *Authenticator apps*.
+      - Under **If a user does not yet have a registered MFA device**, select
+        *Require them to register an MFA device at sign in*.
+  - Under the **Authentication** tab in IAM Identity Center settings, configure
+    the **Standard authentication** to *Send email OTP for users created from
+    API*. This will make sure invitation emails are sent to the users when
+    created using terraform or other tooling.
+- Some tools like aws-nuke require the AWS account to have an alias set before
+  operating on the account. Set an account alias in the IAM Dashboard, refer
+  https://docs.aws.amazon.com/IAM/latest/UserGuide/console_account-alias.html.
+  It can be set to `fluxcd` or edited if needed in the future.
+
+The above covers the initial setup. Further account setup will be done by code
+as described in the following sections.
+
+## Account management
+
+After the initial setup, the account can be managed using terraform
+configurations for provisioning and maintaining all the resources.
+
+`main.tf` contains terraform configuration for creating IAM Identity Center
+permission sets, groups using the permission sets, their association with the
+AWS account, users for web console access, IAM Identity providers which are used
+in the tests for authenticating with federated identities and assuming roles
+with permissions needed for running the tests.
+
+For first time setup, an IAM user can be created manually with the administrator
+access to apply the configurations in `main.tf`. This will create the user
+accounts who can log in and use the account.
+
+**NOTE:** Due to a limitation in the AWS Identity Center API, the user accounts
+created via API require explicit email verification. Refer
+https://github.com/hashicorp/terraform-provider-aws/issues/28102 for details.
+Due to this, after creating a new user, an administrator needs to go to the
+user's page and click on **Send email verification link** button.
+
+After applying the configuration, the IAM user can be deleted and the created
+non-root users can be used to manage the account. Also see
+https://docs.aws.amazon.com/signin/latest/userguide/iam-id-center-sign-in-tutorial.html
+for details about AWS access portal sign in.
+
+The account can be managed by updating the terraform code and regularly applying
+the changes using terraform in a GitHub actions workflow. Updates to users and
+resources in the account can be go through the usual GitHub pull request
+workflow.

accounts/aws/main.tf

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+data "aws_caller_identity" "current" {}
+data "aws_ssoadmin_instances" "current" {}
+
+# Create a permission set for administrator access.
+resource "aws_ssoadmin_permission_set" "admin" {
+  name             = "AdministratorAccess"
+  instance_arn     = tolist(data.aws_ssoadmin_instances.current.arns)[0]
+  description      = "To be used to grant administrator access to users and groups."
+  session_duration = "PT8H"
+  # TODO: Decide and add tags.
+}
+
+# Create a group for administrators.
+resource "aws_identitystore_group" "admin" {
+  identity_store_id = tolist(data.aws_ssoadmin_instances.current.identity_store_ids)[0]
+  display_name      = "Admin"
+  description       = "Admin Group"
+}
+
+# Assign the admin group and permission set.
+resource "aws_ssoadmin_account_assignment" "admin_account_assignment" {
+  instance_arn       = tolist(data.aws_ssoadmin_instances.current.arns)[0]
+  permission_set_arn = aws_ssoadmin_permission_set.admin.arn
+
+  principal_id   = aws_identitystore_group.admin.group_id
+  principal_type = "GROUP"
+
+  target_id   = data.aws_caller_identity.current.account_id
+  target_type = "AWS_ACCOUNT"
+}
+
+# Attach a AdministratorAccess managed policy to the administrator permission
+# set.
+# NOTE: Since this attachment affects accounts the permission set is associated
+# with, it has to depends on the account assignment.
+resource "aws_ssoadmin_managed_policy_attachment" "admin" {
+  depends_on = [aws_ssoadmin_account_assignment.admin_account_assignment]
+
+  instance_arn       = tolist(data.aws_ssoadmin_instances.current.arns)[0]
+  managed_policy_arn = "arn:aws:iam::aws:policy/AdministratorAccess"
+  permission_set_arn = aws_ssoadmin_permission_set.admin.arn
+}
+
+# Create user and assign a group.
+resource "aws_identitystore_user" "darkowlzz" {
+  identity_store_id = tolist(data.aws_ssoadmin_instances.current.identity_store_ids)[0]
+
+  display_name = "Sunny"
+  user_name    = "darkowlzz"
+
+  name {
+    given_name  = "Sunny"
+    family_name = "Sunny"
+  }
+
+  emails {
+    value   = "[email protected]"
+    primary = true
+  }
+}
+resource "aws_identitystore_group_membership" "darkowlzz_admin" {
+  identity_store_id = tolist(data.aws_ssoadmin_instances.current.identity_store_ids)[0]
+  group_id          = aws_identitystore_group.admin.group_id
+  member_id         = aws_identitystore_user.darkowlzz.user_id
+}
+
+# Register GitHub OIDC identity provider.
+resource "aws_iam_openid_connect_provider" "github" {
+  url = "https://token.actions.githubusercontent.com"
+
+  client_id_list = [
+    "sts.amazonaws.com",
+  ]
+
+  # For obtaining the thumbprint, refer
+  # https://docs.aws.amazon.com/IAM/latest/UserGuide/id_roles_providers_create_oidc_verify-thumbprint.html.
+  # Another easier way to obtain this is from the AWS IAM Identity Provider web
+  # console. When a provider is added through the web console, the thumbprint is
+  # optional. AWS automatically obtains it and shows it in the console.
+  thumbprint_list = ["1b511abead59c6ce207077c0bf0e0043b1382612"]
+
+  # TODO: Decide and add tags.
+}