Authenticate to AWS Using OIDC for Downloading and Verification of Images

This guide explains how to configure OpenID Connect (OIDC) authentication to download Kloudfuse container images from AWS ECR and verify their signatures in CI/CD pipelines without managing long-lived AWS credentials.

Overview

When downloading Kloudfuse container images in CI/CD pipelines, you need AWS ECR access to pull images and AWS KMS access to verify their signatures. Instead of storing AWS credentials (access keys) in your CI/CD environment, you can use OIDC to establish a trust relationship between your CI/CD provider (like GitLab) and AWS.

Benefits of OIDC Authentication

• No long-lived credentials - No AWS access keys to manage or rotate
• Automatic token generation - CI/CD provider generates short-lived tokens automatically
• Fine-grained access control - Limit access to specific projects, branches, or jobs
• Enhanced security - Tokens expire automatically and cannot be reused
• Audit trail - AWS CloudTrail logs show which jobs assumed roles

Architecture

The OIDC authentication flow works as follows:

┌─────────────────┐         ┌──────────────────┐         ┌─────────────┐
│   GitLab CI/CD  │         │   AWS STS        │         │  AWS KMS    │
│   Pipeline      │         │                  │         │             │
└────────┬────────┘         └────────┬─────────┘         └──────┬──────┘
         │                           │                          │
         │ 1. Request OIDC token     │                          │
         ├──────────────────────────>│                          │
         │                           │                          │
         │ 2. Return JWT token       │                          │
         │<──────────────────────────┤                          │
         │                           │                          │
         │ 3. AssumeRoleWithWebIdentity                         │
         │    (with OIDC token)      │                          │
         ├──────────────────────────>│                          │
         │                           │                          │
         │ 4. Validate token against │                          │
         │    OIDC provider          │                          │
         │                           │                          │
         │ 5. Return temporary       │                          │
         │    AWS credentials        │                          │
         │<──────────────────────────┤                          │
         │                           │                          │
         │ 6. Use credentials to call kms:Verify               │
         ├─────────────────────────────────────────────────────>│
         │                           │                          │
         │ 7. Signature verification result                     │
         │<─────────────────────────────────────────────────────┤

Setup Process

Setting up OIDC authentication requires configuring both AWS and your CI/CD provider.

Step 1: Create OIDC Provider in AWS

First, establish trust between AWS and your CI/CD platform’s OIDC provider.

For GitLab (Self-Hosted or GitLab.com)

1. Navigate to AWS IAM Console → Identity Providers → Add Provider

2. Configure the OIDC provider:

• Provider Type: OpenID Connect
  • Provider URL: Your GitLab OIDC endpoint
  • Audience: Your GitLab instance URL

Example for GitLab Corporate Instance:

• Provider URL: https://gitlab-oidc-config.s3.us-west-2.amazonaws.com
• Audience: https://gitlab.example.com

Example for GitLab.com:

• Provider URL: https://gitlab.com
• Audience: https://gitlab.com

Step 2: Create and Attach IAM Policies for ECR and KMS Access

Create and attach policies that grant permissions to pull Kloudfuse container images from ECR and verify their signatures.

For ECR Access: Attach both of these AWS managed policies:

AmazonEC2ContainerRegistryReadOnly

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "ecr:GetAuthorizationToken",
                "ecr:BatchCheckLayerAvailability",
                "ecr:GetDownloadUrlForLayer",
                "ecr:GetRepositoryPolicy",
                "ecr:DescribeRepositories",
                "ecr:ListImages",
                "ecr:DescribeImages",
                "ecr:BatchGetImage",
                "ecr:GetLifecyclePolicy",
                "ecr:GetLifecyclePolicyPreview",
                "ecr:ListTagsForResource",
                "ecr:DescribeImageScanFindings"
            ],
            "Resource": "*"
        }
    ]
}

AmazonEC2ContainerRegistryPullOnly

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "ecr:GetAuthorizationToken",
                "ecr:BatchGetImage",
                "ecr:GetDownloadUrlForLayer",
                "ecr:BatchImportUpstreamImage"
            ],
            "Resource": "*"
        }
    ]
}

For KMS Access: Create a custom policy for KMS signature verification:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "KMSSignatureVerification",
            "Effect": "Allow",
            "Action": [
                "kms:GetPublicKey",
                "kms:Verify",
                "kms:DescribeKey"
            ],
            "Resource": [
                "arn:aws:kms:us-west-2:502496443919:alias/kfuse-cosign-signing-key"
            ]
        }
    ]
}

Step 3: Create IAM Role with OIDC Trust Relationship

Create an IAM role that can be assumed by your CI/CD jobs using OIDC tokens.

1. Navigate to AWS IAM Console → Roles → Create Role
2. Select Web Identity as the trusted entity type
3. Configure the trust relationship:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Principal": {
                "Federated": "arn:aws:iam::YOUR_AWS_ACCOUNT_ID:oidc-provider/gitlab.example.com"
            },
            "Action": "sts:AssumeRoleWithWebIdentity",
            "Condition": {
                "StringEquals": {
                    "gitlab.example.com:aud": "https://gitlab.example.com"
                },
                "StringLike": {
                    "gitlab.example.com:sub": "project_path:your-organization/*"
                }
            }
        }
    ]
}

Step 4: Configure CI/CD Pipeline

Configure your CI/CD pipeline to use the OIDC role for AWS authentication.

GitLab CI/CD Example

verify-kfuse-image:
  stage: verify
  image: alpine:latest

variables:
    IMAGE_NAME: ui
    IMAGE_TAG: "0.1.0-b2274ac0"
    COSIGN_VERSION: "v3.0.3"
    KMS_KEY: "awskms:///arn:aws:kms:us-west-2:502496443919:alias/kfuse-cosign-signing-key"
    AWS_ROLE_ARN: "arn:aws:iam::YOUR_AWS_ACCOUNT_ID:role/KloudfuseImageVerificationRole"
    AWS_DEFAULT_REGION: "us-west-2"

id_tokens:
    GITLAB_OIDC_TOKEN:
      aud: https://gitlab.example.com

before_script:
    - apk add --no-cache curl aws-cli jq
    - curl -sSfL "https://github.com/sigstore/cosign/releases/download/${COSIGN_VERSION}/cosign-linux-amd64" -o /usr/local/bin/cosign
    - chmod +x /usr/local/bin/cosign
    - |
      echo "Assuming AWS role using OIDC..."

STS_RESPONSE=$(aws sts assume-role-with-web-identity \
        --role-arn "${AWS_ROLE_ARN}" \
        --role-session-name "gitlab-ci-${CI_PROJECT_NAME}-${CI_PIPELINE_ID}" \
        --web-identity-token "${GITLAB_OIDC_TOKEN}" \
        --duration-seconds 3600)

export AWS_ACCESS_KEY_ID=$(echo "$STS_RESPONSE" | jq -r '.Credentials.AccessKeyId')
      export AWS_SECRET_ACCESS_KEY=$(echo "$STS_RESPONSE" | jq -r '.Credentials.SecretAccessKey')
      export AWS_SESSION_TOKEN=$(echo "$STS_RESPONSE" | jq -r '.Credentials.SessionToken')

echo "✅ Successfully authenticated to AWS"
  script:
    - |
      IMAGE_REF="502496443919.dkr.ecr.us-west-2.amazonaws.com/kfuse/${IMAGE_NAME}:${IMAGE_TAG}"

echo "Logging in to Kloudfuse ECR..."
      aws ecr get-login-password --region us-west-2 | \
        docker login --username AWS --password-stdin 502496443919.dkr.ecr.us-west-2.amazonaws.com

echo "Pulling image ${IMAGE_REF}..."
      docker pull "${IMAGE_REF}"

echo "Verifying signature for ${IMAGE_REF}..."
      if cosign verify --key "${KMS_KEY}" "${IMAGE_REF}"; then
        echo "✅ Image signature verified successfully"
      else
        echo "⚠️  Warning: Image signature verification FAILED"
      fi

echo "✅ Image pulled and verified successfully"

Verification and Testing

Test the Pipeline

1. Commit the pipeline configuration to your GitLab repository
2. Run the pipeline manually or via a commit
3. Check the job logs for:

Assuming AWS role using OIDC...
✅ Successfully authenticated to AWS
Logging in to Kloudfuse ECR...
Login Succeeded
Pulling image 502496443919.dkr.ecr.us-west-2.amazonaws.com/kfuse/ui:0.1.0-b2274ac0...
0.1.0-b2274ac0: Pulling from kfuse/ui
✅ Image pulled and verified successfully

Troubleshooting

• "Not authorized to perform sts:AssumeRoleWithWebIdentity"

  • Cause: OIDC provider not configured or trust relationship incorrect
  • Solution: Verify the OIDC provider ARN in the role’s trust relationship matches the provider created in Step 1

• "Access denied" with audience mismatch

  • Cause: The aud claim in the OIDC token doesn’t match the trust relationship
  • Solution: Ensure id_tokens.GITLAB_OIDC_TOKEN.aud in your pipeline matches the audience in the trust relationship condition

• "Access denied" with subject mismatch

  • Cause: The sub claim in the OIDC token doesn’t match the trust relationship condition
  • Solution: Verify the StringLike condition in the trust relationship matches your GitLab project path

• "Token has expired"

  • Cause: OIDC token lifetime exceeded
  • Solution: OIDC tokens are typically valid for 5-10 minutes. Ensure assume-role-with-web-identity runs early in the job

• "Access Denied" when calling KMS operations

  • Cause: IAM role doesn’t have KMS permissions
  • Solution: Verify the KMS policy from Step 2 is attached to the role

Debug OIDC Token Claims

To inspect what claims GitLab is sending in the OIDC token:

echo "${GITLAB_OIDC_TOKEN}" | cut -d. -f2 | base64 -d 2>/dev/null | jq .

{
  "aud": "https://gitlab.example.com",
  "sub": "project_path:your-organization/your-project:ref:refs/heads/main",
  "iss": "https://gitlab.example.com",
  "exp": 1735123456,
  "iat": 1735123156,
  "jti": "abc123..."
}

Security Best Practices

1. Minimize trust scope - Use specific StringLike conditions to limit which projects/branches can assume the role
2. Short session duration - Use the minimum --duration-seconds needed for your job (typically 3600 = 1 hour)
3. Least privilege - Grant only the KMS permissions needed (GetPublicKey, Verify, DescribeKey)
4. Monitor CloudTrail - Set up alerts for unexpected AssumeRoleWithWebIdentity events
5. Rotate OIDC providers - Periodically review and update OIDC provider configurations
6. Use session names - Include pipeline/job identifiers in session names for better audit trails

Advanced Configurations

Multiple AWS Accounts (Development, Staging, Production)

Use different IAM roles per environment:

.verify-template:
  stage: verify
  # ... (common configuration)
  script:
    - |
      case "${CI_ENVIRONMENT_NAME}" in
        production)
          AWS_ROLE_ARN="arn:aws:iam::111111111111:role/KfuseImageVerify-Prod"
          ;;
        staging)
          AWS_ROLE_ARN="arn:aws:iam::222222222222:role/KfuseImageVerify-Staging"
          ;;
        development)
          AWS_ROLE_ARN="arn:aws:iam::333333333333:role/KfuseImageVerify-Dev"
          ;;
      esac

# ... (assume role and verify)

verify-prod:
  extends: .verify-template
  environment: production
  only:
    - main

verify-staging:
  extends: .verify-template
  environment: staging
  only:
    - staging

Cross-Account KMS Access

If your AWS account differs from Kloudfuse’s KMS account (502496443919), you need to:

1. Ensure the KMS key policy allows your account
2. Add kms:* permissions for the key ARN in your IAM policy

Related Documentation

• Verify Container Image Signatures - Basic signature verification guide
• GitLab AWS Integration - GitLab’s OIDC documentation
• AWS OIDC Identity Providers - AWS IAM documentation
• Cosign Documentation - Cosign signature verification

Support

For questions or issues:

• Kloudfuse Support: support@kloudfuse.com
• AWS IAM/OIDC Issues: Consult AWS Support or your AWS Solutions Architect
• GitLab OIDC Issues: GitLab Documentation