Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx agentmods add skills/orcaqubits/agentic-commerce-skills-plugins/a2a-authenticationnpx skills add OrcaQubits/agentic-commerce-skills-plugins --skill a2a-authenticationgit clone --depth 1 https://github.com/OrcaQubits/agentic-commerce-skills-pluginsWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/orcaqubits/agentic-commerce-skills-plugins/a2a-authentication)<a href="https://agentmods.dev/skills/orcaqubits/agentic-commerce-skills-plugins/a2a-authentication"><img src="https://agentmods.dev/badge/skills/orcaqubits/agentic-commerce-skills-plugins/a2a-authentication.svg" alt="Measured on agentmods" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5 | $0.00047 | $0.00985 |
| Opus 5 | $0.00023 | $0.00492 |
| Sonnet 5 | $0.00009 | $0.00197 |
| Haiku 4.5 | $0.00005 | $0.00098 |
Grade A, and why
a2a-authentication scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 5d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 111 lines — stays where its author put it; the contents beside it link to each section on GitHub.
A2A Authentication
Before writing code
Fetch live docs:
- Fetch
https://a2a-protocol.org/latest/specification/for the authentication and security section - Web-search
site:github.com a2aproject A2A authentication security schemesfor auth scheme details - Web-search
site:github.com a2aproject a2a-samples authenticationfor auth implementation examples - Fetch SDK docs for authentication middleware and client credential handling
Conceptual Architecture
Why Authentication Matters
In multi-agent systems, agents must verify each other's identity and authorize access:
- Server agents need to know who's calling them and whether they're authorized
- Client agents need to present valid credentials to access server agents
- Agent Cards declare what authentication is required upfront
Five Security Schemes
A2A supports the same security scheme types as OpenAPI 3.0:
1. API Key (apiKey)
A static key sent in a header or query parameter.
- Best for: Internal agents, simple integrations, development
- Agent Card declares: Header name and location
- Client provides: The key value in the specified header
2. HTTP Bearer (http with scheme: bearer)
A bearer token (JWT or opaque) in the Authorization header.
- Best for: Token-based auth, service-to-service with JWTs
- Agent Card declares: Bearer scheme, optional format hint
- Client provides:
Authorization: Bearer <token>
3. OAuth 2.0 (oauth2)
Standard OAuth 2.0 flows for token acquisition.
- Best for: Production systems, fine-grained scopes, delegated access
- Agent Card declares: OAuth flows (clientCredentials, authorizationCode), token URL, scopes
- Client provides: Access token obtained from the OAuth server
Common flow for agent-to-agent: Client Credentials (machine-to-machine, no user involvement).
4. OpenID Connect (openIdConnect)
OIDC discovery-based authentication.
- Best for: Enterprise systems with identity providers, SSO environments
- Agent Card declares: OIDC discovery URL (
openIdConnectUrl) - Client provides: Token obtained via OIDC flow
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 5d ago First seen · 111 lines · 47 tokens per session scan A 2411bf030d7c
a2a-authentication is a skill published in the GitHub repository OrcaQubits/agentic-commerce-skills-plugins (39 stars, last pushed 3mo ago), licensed MIT. It adds 47 tokens to every session and 985 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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