Cross-Cloud Security: Navigating Identity Federation and Forensics Across AWS and GCP

More companies are going multi-cloud - and fast. AWS and GCP sit at the centre of that shift. The upside?
Flexibility and speed. The downside? Identity and security suddenly get a lot more complicated.

Federating identity across two fundamentally different clouds sounds great in theory. One login to rule them all.
But in practice, it’s messy. Mapping roles, aligning policies, and securing access without creating gaps
takes more than just connecting an IdP and calling it a day.

And then there’s forensics. When something goes wrong - and it will - you need to investigate across
two separate platforms with different tools, logs, and assumptions.

This briefing focuses on the real-world friction points cloud leaders face with identity federation and
incident response across AWS and GCP, and how to navigate them without burning out your team.

1. Identity Federation 101 – What It Is and Why It’s Tricky

At a high level, identity federation means users log in once, usually through a central identity provider (IdP),
and get access to services across multiple cloud providers. One identity, multiple environments.

That’s the promise, anyway.

How It Works in AWS

Federation in AWS is built on IAM roles, AWS STS (Security Token Service), and tools like AWS SSO.
It supports SAML and OIDC protocols. After authentication, users are granted temporary credentials
tied to scoped roles.

How It Works in GCP

GCP also supports SAML and OIDC, but it handles federation through IAM policies, Cloud Identity-Aware Proxy (IAP),
and context-aware access. Access is controlled via IAM bindings, often with environmental conditions.

The Catch

These models don’t map perfectly. Attributes, trust relationships, and access controls differ. What’s “normal”
in AWS might be unsupported, or worse, misinterpreted - in GCP.

2. Identity Federation Isn’t Plug and Play

Let’s talk about what typically breaks in production.

a. Policy Drift and Permission Gaps

Roles in AWS vs. policies in GCP = two different languages. Even if your IdP mapping looks fine, users can
end up over-permissioned in one cloud or locked out in another.

b. Same Protocol, Different Results

SAML and OIDC support ≠ consistency. Attribute mapping, group claims, or token TTLs behave differently.
A small config mismatch can cause access failures or unintended admin access.

c. Role Mapping Requires Precision

In AWS, a claim maps to a role. In GCP, to a policy binding. One typo, one forgotten scope, and your federated
model could expose sensitive data across both platforms.

3. How to Lock Down Identity Across AWS and GCP

a. Use One IdP to Rule Them All

Standardise identity through a single source - Azure AD, Okta, or Google Workspace. Integrate with AWS SSO
and GCP IAP to centralise login and mapping.

Pro tip: Leverage detailed SAML assertions to tightly control elevated permissions across environments.

b. Zero Trust Isn’t a Buzzword

• In AWS: Use condition keys (like source IP or MFA status).
  
• In GCP: Use context-aware access (device trust, location).
  Never assume trust across clouds—validate everything.

c. Log Everything—and Correlate It

Both clouds generate powerful audit logs:

• AWS: CloudTrail, GuardDuty
  
• GCP: Audit Logs, SCC
  But if you're not pulling them into a single view, you're flying blind. Use a central SIEM like Splunk,
  Datadog, or Chronicle.
  

4. Forensics Across Clouds: What Happens When It Hits the Fan

a. Your IR Team Needs Bilingual Skills

If a user gets compromised in AWS, your analysts should be able to trace that identity across both clouds.

Tools to know:

• AWS: CloudTrail, GuardDuty, VPC Flow Logs
  
• GCP: Cloud Audit Logs, SCC, VPC Flow Logs
  

b. Centralise Detection and Correlation

Incidents don’t respect cloud boundaries. Your detection stack should pull logs from both and create correlated alerts.

5. What Cloud Leaders Should Do - Now!

✅ a. Unify Your Identity Stack

Start with one IdP. Keep mappings consistent. Minimise local accounts.

✅ b. Don’t Ignore Logs

Centralise logging across AWS and GCP. Build alert rules that reflect federated identities.

✅ c. Create a Cross-Cloud IR Playbook

If an incident starts in GCP and spreads to AWS, does your team know what to do? Write it down. Test it quarterly.

✅ d. Automate What You Can

Use Cloud Functions or Lambda to trigger actions on risky behaviour. Consider AI-assisted tools to flag
anomalies before they become problems.

🧠 Final Thought: Multi-Cloud Isn’t Easy, But It Can Be Secure

Federating identity and managing forensics across AWS and GCP is hard - but it’s not impossible. It just takes structure.

With a unified identity model, a real Zero Trust posture, and a detection system that spans cloud boundaries,
you can cut through the noise and catch missteps before they become breaches.

Because at the end of the day, it’s not just the federation protocol that keeps you safe - it’s the discipline behind the process.

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