OIDC authentication for CI/CD in Terraform - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does OIDC stand for and why is it used in CI/CD pipelines?

OIDC stands for OpenID Connect. It is used in CI/CD pipelines to securely authenticate and authorize workflows without storing long-lived credentials, improving security by using short-lived tokens.

intermediate

How does OIDC improve security in Terraform workflows?

OIDC allows Terraform workflows to request temporary tokens from an identity provider, avoiding hardcoded secrets. This reduces risk of credential leaks and simplifies access management.

intermediate

In Terraform, which resource or provider is commonly configured to use OIDC for authentication?

Terraform often uses the 'aws' provider configured with an OIDC role assumption or the 'google' provider with workload identity federation to authenticate using OIDC tokens.

beginner

What is the role of the identity provider (IdP) in OIDC authentication for CI/CD?

The identity provider issues ID tokens after verifying the workflow's identity. These tokens prove the workflow's identity to cloud providers, enabling secure access without static credentials.

advanced

Explain the concept of 'workload identity federation' in the context of OIDC and Terraform.

Workload identity federation lets Terraform workflows authenticate to cloud providers by exchanging OIDC tokens from the CI/CD system, avoiding the need for service account keys or secrets.

What is the main benefit of using OIDC authentication in CI/CD pipelines?

A Enable manual approvals

B Increase build speed

C Avoid storing long-lived credentials

D Reduce code size

OIDC allows workflows to authenticate using short-lived tokens, avoiding the need to store long-lived credentials.

Which Terraform provider commonly supports OIDC authentication for AWS?

A aws

B random

C azure

D google

The 'aws' provider supports OIDC role assumption for authentication.

In OIDC, what does the identity provider (IdP) issue to prove identity?

A ID token

B Access key

C Password

D SSH key

The IdP issues an ID token that proves the identity of the requester.

What is workload identity federation used for in Terraform CI/CD workflows?

A To store secrets securely

B To authenticate using OIDC tokens without service account keys

C To speed up deployments

D To encrypt Terraform state files

Workload identity federation allows authentication using OIDC tokens, avoiding the need for static service account keys.

Which of the following is NOT a benefit of OIDC in CI/CD?

A Improved security

B Simplifies access management

C Eliminates need for manual credential rotation

D Requires storing static passwords

OIDC reduces or eliminates the need to store static passwords, so option B is NOT a benefit.

Describe how OIDC authentication works in a CI/CD pipeline using Terraform.

Think about the token flow and how Terraform gains access securely.

Explain the advantages of using workload identity federation with OIDC in Terraform CI/CD workflows.

Focus on security and credential handling improvements.

Practice

1. What is the main benefit of using OIDC authentication in CI/CD pipelines with Terraform?

easy

A. It disables all access restrictions for faster builds.

B. It automatically deploys code without any manual approval.

C. It replaces Terraform with a different infrastructure tool.

D. It allows secure authentication without storing passwords in the pipeline.

Solution

1. Step 1: Understand OIDC purpose in CI/CD

   OIDC provides a secure way for pipelines to prove identity without passwords.

2. Step 2: Connect to Terraform usage

   Terraform can create roles that trust OIDC tokens, avoiding password storage.

3. Final Answer:

   It allows secure authentication without storing passwords in the pipeline. -> Option D

4. Quick Check:

   OIDC = passwordless secure authentication [OK]

Hint: OIDC means no passwords needed in CI/CD [OK]

Common Mistakes:

• Thinking OIDC automates deployment without approval
• Confusing OIDC with replacing Terraform
• Assuming OIDC disables access controls

2. Which Terraform resource block correctly defines an IAM role trusting GitHub Actions OIDC provider?

easy

A. resource "aws_iam_role" "github_oidc_role" {
assume_role_policy = jsonencode({
Version = "2012-10-17",
Statement = [{
Effect = "Allow",
Principal = { Federated = "arn:aws:iam::123456789012:oidc-provider/token.actions.githubusercontent.com" },
Action = "sts:AssumeRoleWithWebIdentity"
}]
})
}

B. resource "aws_iam_role" "github_oidc_role" {
assume_role_policy = jsonencode({
Version = "2012-10-17",
Statement = [{
Effect = "Allow",
Principal = { Service = "github.com" },
Action = "sts:AssumeRole"
}]
})
}

C. resource "aws_iam_role" "github_oidc_role" {
assume_role_policy = jsonencode({
Version = "2012-10-17",
Statement = [{
Effect = "Allow",
Principal = { AWS = "arn:aws:iam::123456789012:root" },
Action = "sts:AssumeRoleWithWebIdentity"
}]
})
}

D. resource "aws_iam_role" "github_oidc_role" {
assume_role_policy = jsonencode({
Version = "2012-10-17",
Statement = [{
Effect = "Allow",
Principal = { Federated = "arn:aws:iam::123456789012:oidc-provider/github.com" },
Action = "sts:AssumeRoleWithWebIdentity"
}]
})
}

Solution

1. Step 1: Identify correct OIDC provider ARN format

   The OIDC provider ARN for GitHub Actions uses 'token.actions.githubusercontent.com'.

2. Step 2: Check assume_role_policy structure

   The policy must allow 'sts:AssumeRoleWithWebIdentity' with Principal as Federated and correct ARN.

3. Final Answer:

   The resource block with Federated principal using 'token.actions.githubusercontent.com' and 'sts:AssumeRoleWithWebIdentity' action. -> Option A

4. Quick Check:

   Correct OIDC ARN + sts:AssumeRoleWithWebIdentity = resource "aws_iam_role" "github_oidc_role" { assume_role_policy = jsonencode({ Version = "2012-10-17", Statement = [{ Effect = "Allow", Principal = { Federated = "arn:aws:iam::123456789012:oidc-provider/token.actions.githubusercontent.com" }, Action = "sts:AssumeRoleWithWebIdentity" }] }) } [OK]

Hint: OIDC provider ARN uses token.actions.githubusercontent.com [OK]

Common Mistakes:

• Using Service principal instead of Federated
• Wrong OIDC provider ARN format
• Using sts:AssumeRole instead of sts:AssumeRoleWithWebIdentity

3. Given this Terraform snippet for an IAM role trust policy, what is the effect of the condition block?

condition = {
  StringEquals = {
    "token.actions.githubusercontent.com:sub" = "repo:myorg/myrepo:ref:refs/heads/main"
  }
}

medium

A. Allows any GitHub repo to assume the role.

B. Restricts role assumption to the main branch of myorg/myrepo only.

C. Blocks all role assumptions from GitHub Actions.

D. Allows only forks of myorg/myrepo to assume the role.

Solution

1. Step 1: Understand the condition key

   The condition uses 'token.actions.githubusercontent.com:sub' to specify the GitHub repo and branch.

2. Step 2: Interpret the value

   The value 'repo:myorg/myrepo:ref:refs/heads/main' restricts access to the main branch of that repo only.

3. Final Answer:

   Restricts role assumption to the main branch of myorg/myrepo only. -> Option B

4. Quick Check:

   Condition limits to specific repo and branch = Restricts role assumption to the main branch of myorg/myrepo only. [OK]

Hint: Condition with repo and ref limits branch access [OK]

Common Mistakes:

• Ignoring the branch restriction in condition
• Assuming condition allows all repos
• Confusing forks with original repo access

4. You wrote this Terraform assume_role_policy but your CI/CD pipeline fails to authenticate:

{
  "Version": "2012-10-17",
  "Statement": [{
    "Effect": "Allow",
    "Principal": { "Federated": "arn:aws:iam::123456789012:oidc-provider/github.com" },
    "Action": "sts:AssumeRoleWithWebIdentity"
  }]
}

What is the most likely error?

medium

A. The Principal should use 'Service' instead of 'Federated'.

B. The Action should be 'sts:AssumeRole' instead of 'sts:AssumeRoleWithWebIdentity'.

C. The OIDC provider ARN is incorrect; it should be 'token.actions.githubusercontent.com'.

D. The Version date is invalid and must be updated.

Solution

1. Step 1: Check the OIDC provider ARN

   The ARN 'arn:aws:iam::123456789012:oidc-provider/github.com' is incorrect for GitHub Actions.

2. Step 2: Identify correct ARN for GitHub Actions

   The correct ARN uses 'token.actions.githubusercontent.com' as the OIDC provider host.

3. Final Answer:

   The OIDC provider ARN is incorrect; it should be 'token.actions.githubusercontent.com'. -> Option C

4. Quick Check:

   Wrong OIDC ARN causes auth failure = The OIDC provider ARN is incorrect; it should be 'token.actions.githubusercontent.com'. [OK]

Hint: Check OIDC ARN spelling carefully for GitHub Actions [OK]

Common Mistakes:

• Using 'sts:AssumeRole' instead of 'sts:AssumeRoleWithWebIdentity'
• Confusing Federated with Service principal
• Ignoring ARN format for OIDC provider

5. You want to create a Terraform IAM role for GitHub Actions that only allows workflows from the 'release' branch of 'myorg/myrepo' to assume it. Which condition block correctly enforces this restriction?

hard

A. {
"StringEquals": {
"token.actions.githubusercontent.com:sub": "repo:myorg/myrepo:ref:refs/heads/release"
}
}

B. {
"StringLike": {
"token.actions.githubusercontent.com:sub": "repo:myorg/myrepo:ref:refs/heads/*"
}
}

C. {
"StringEquals": {
"token.actions.githubusercontent.com:aud": "sts.amazonaws.com"
}
}

D. {
"StringNotEquals": {
"token.actions.githubusercontent.com:sub": "repo:myorg/myrepo:ref:refs/heads/main"
}
}

Solution

1. Step 1: Understand the condition key and value

   To restrict to the 'release' branch, the condition must match 'repo:myorg/myrepo:ref:refs/heads/release'.

2. Step 2: Choose correct operator

   'StringEquals' ensures exact match, so only 'release' branch is allowed.

3. Final Answer:

   The condition block with StringEquals matching 'repo:myorg/myrepo:ref:refs/heads/release'. -> Option A

4. Quick Check:

   Exact branch match uses StringEquals with correct ref [OK]

Hint: Use StringEquals with exact repo and branch ref [OK]

Common Mistakes:

• Using StringLike with wildcard allowing all branches
• Checking audience (aud) instead of subject (sub)
• Using StringNotEquals which excludes main but allows others