Using Service account Key to consume GCS bucket

[avindia]

I see this is very common use case where Onprem App or API client on another CSP like AWS wanted to access Google cloud storage using API Call. Need explanation on Authentication methods used in GCP

1. API Keys 
2. OuTh2.0 Client ID (  Uses Service account ??) 
3. Service account Key 

Queries below from configuration and security point of view 

1. Need help with to understand difference between Service Account Key and OAuth2.0 Client ID from Pros and Cons.
2. In case of Service Account Keys - Document says Service account uses JSON File ( JWT token) which is Pvt key and you can download. Install client library and configure environment variable.However same time document says Service account use RSA Key pair and you just need to upload Pub key to GCP platform. PVT key is used to request access token and so on ..

"Using a service account key to sign a JSON Web Token (JWT) and exchange it for an access token"

Need help with

• Sequence flow on how Service account is used to access GCP bucket from Onprem/Other Cloud
• How to secure pvt key ( secret management)
• How to rotate Key on expiration with automation

[L1kruzing · Accepted solution]

Hey, If you need to hook up your stuff to Google Cloud Storage from AWS or on-prem, here’s what you do:

• API Keys: Meh, not secure, skip it.
• OAuth 2.0 Client ID: Cool if users are involved, but overkill for server stuff.
• Service Account Keys: This is the one. Grab the JSON key, plug it in, and you’re good.

Service Account Keys:

• 👍 Perfect for server-to-server stuff, no manual steps needed.
• 👎 If the key leaks, you're screwed, so keep it tight.

Lock It down:

• Use a secret manager, don’t leave keys lying around.
• Tighten access, only who needs it, gets it.
• Rotate keys with automation. Think Terraform or scripts, no manual nonsense.

[avindia]

Thanks This helps ! may be I will raise another query on difference  when you use OAuth and OIDC as that is another big enigma to me