add idp, oidc integration terraform configs

terraform/aws-identity-providers.tf

@@ -0,0 +1,84 @@
+# references: 
+#   https://docs.github.com/en/actions/deployment/security-hardening-your-deployments/about-security-hardening-with-openid-connect
+#   https://docs.aws.amazon.com/IAM/latest/UserGuide/id_roles_create_for-idp_oidc.html#idp_oidc_Create_GitHub
+#   https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/iam_openid_connect_provider
+#   https://github.com/aws-actions/configure-aws-credentials#configure-aws-credentials-for-github-actions
+
+locals {
+  # prefix used in custom resource names
+  naming_prefix = "github-incubator-actions-terraform"
+
+  # AWS receives the call from Actions, so is registered as the 'aud' of the id token
+  oidc_aws_audience = "sts.amazonaws.com"
+
+  # well-known identity provider FQDN
+  oidc_github_idp = "token.actions.githubusercontent.com"
+
+  # repository which will be authorized to assume IAM role
+  github_repo_name = "incubator"
+
+  # branch which will be authorized to assume IAM role
+  github_branch_name = "main"
+
+  # aws actions creds provider will use this schema for the 'sub' of the id token
+  oidc_github_subject = "repo:hackforla/${local.github_repo_name}:ref:refs/heads/${local.github_branch_name}"
+}
+
+data "aws_caller_identity" "current" {}
+
+resource "aws_iam_openid_connect_provider" "github_actions" {
+  url = "https://${local.oidc_github_idp}"
+
+  client_id_list = [
+    local.oidc_aws_audience
+  ]
+
+  thumbprint_list = ["1b511abead59c6ce207077c0bf0e0043b1382612"]
+}
+
+resource "aws_iam_role" "github_actions_oidc" {
+  name = "${local.naming_prefix}-deployer"
+
+  managed_policy_arns = [
+    # TODO: replace admin with the correct scopes, once known
+    "arn:aws:iam::aws:policy/AdministratorAccess"
+  ]
+
+  assume_role_policy = jsonencode({
+    "Version" : "2012-10-17",
+    "Statement" : [
+      {
+        "Effect" : "Allow",
+        "Principal" : {
+          "Federated" : "arn:aws:iam::${data.aws_caller_identity.current.account_id}:oidc-provider/${local.oidc_github_idp}"
+        },
+        "Action" : "sts:AssumeRoleWithWebIdentity",
+        "Condition" : {
+          "StringEquals" : {
+            "token.actions.githubusercontent.com:aud" : local.oidc_aws_audience,
+            "token.actions.githubusercontent.com:sub" : local.oidc_github_subject
+          }
+        }
+        /** TODO: discuss, update and remove this comment -- there are multiple approaches devops/incubator can
+          *    can use to authorize tokens, including branches/environments with wildcard patterns support e.g. release/*
+          * wildcard example:
+
+                "Condition" : {
+                    "StringLike": {
+                        "token.actions.githubusercontent.com:sub": "repo:octo-org/octo-repo:*"
+                    },
+                    "StringEquals": {
+                        "token.actions.githubusercontent.com:aud": "sts.amazonaws.com"
+                    }
+                }
+
+        */
+      }
+    ]
+  })
+
+  tags = {
+    "app" = "devops-security"
+  }
+
+}