What is a Security Token Service?

A Security Token Service (STS) is a web service that issues, validates, and exchanges security tokens, allowing systems to authenticate and authorize access without repeatedly sharing long-lived secrets.

Why use temporary tokens instead of permanent credentials?

Temporary tokens reduce risk because they automatically expire and can be scoped to specific permissions, limiting the damage if a token is ever leaked or intercepted.

How does an STS relate to federated identity?

In federated identity flows, a user authenticates with an identity provider, and an STS can issue a token that downstream services trust, without those services needing direct access to the original credentials.

Is a Security Token Service the same across all cloud providers?

No, implementations vary — AWS, Azure, and other platforms have their own token issuance services and mechanics, though they share the general concept of exchanging identity proof for a scoped, temporary token.

How is an STS token different from a password?

Unlike a password, an STS-issued token is typically short-lived, scoped to specific permissions, and not meant for long-term reuse, reducing the risk if it's exposed.

Cybersecurity

Security Token Service

Q: What is AWS Security Token Service used for?

AWS STS issues temporary, limited-privilege credentials for accessing AWS resources, commonly used for cross-account access and workloads that assume IAM roles.

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A Security Token Service (STS) is a web service that issues, validates, and exchanges security tokens — such as temporary credentials or identity assertions — allowing systems to authenticate and authorize access without repeatedly sharing…

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Definition

Overview

An STS acts as a trusted intermediary in federated identity and token-based authentication flows: a client authenticates to the STS (often via a separate identity provider), and in return receives a short-lived security token that downstream services can accept as proof of identity or authorization, rather than requiring each service to independently verify the original credentials. This pattern reduces how widely long-lived secrets like passwords or root API keys need to be shared, since temporary tokens can be scoped to specific permissions and expire automatically. A well-known implementation is AWS Security Token Service, which issues temporary, limited-privilege credentials for accessing AWS resources — commonly used for cross-account access, federated login (e.g., via Identity and Access Management (IAM) roles), and workloads running on EC2 or Lambda that need temporary credentials rather than permanent access keys. Similar concepts appear in broader identity standards like OAuth 2.0 token exchange and SAML assertions issued by an identity provider, and the resulting tokens are frequently handled alongside broader Secrets Management practice. Because implementations and exact mechanics vary significantly across vendors and standards, teams should consult vendor-specific documentation (such as AWS's own STS reference) when implementing token exchange flows; broader identity and access patterns are covered in Cloud Security Fundamentals.

Key Features

Issues short-lived, scoped security tokens instead of long-lived secrets
Acts as a trusted intermediary in federated authentication flows
Reduces exposure of permanent credentials across systems
AWS STS is a widely used implementation for temporary AWS credentials
Supports cross-account access and federated identity scenarios
Related to broader standards like OAuth 2.0 token exchange and SAML

Use Cases

Issuing temporary AWS credentials for cross-account resource access

Granting scoped, time-limited access to federated identity provider users

Enabling workloads to assume IAM roles without embedding permanent keys

Supporting single sign-on flows that exchange one token type for another

Reducing the blast radius of leaked credentials through short token lifetimes

Frequently Asked Questions

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