A2a Client

OPAL A2A Client

Use this skill to interact with an OPAL backend that implements the Agent2Agent protocol.

Required Elicitations

Before making any request, obtain these runtime values from the user, environment, or an already verified project config:

• Target endpoint: either an HTTPS base URL such as https://{CNAME} or a full A2A URL such as https://{CNAME}/chat/api/a2a; CLI args win over OPAL_A2A_BASE_URL, OPAL_A2A_CNAME, OPAL_A2A_URL, and OPAL_A2A_CARD_URL.
• Authentication mode: bearer/API key, dynamic OAuth Authorization Code, OAuth2 client credentials, or no request until credentials are supplied.
• Credential source: environment variable name, secret manager reference, dynamic OAuth flow, or user-provided value. The script recognizes OPAL_A2A_TOKEN_ENV and OPAL_A2A_TOKEN; do not echo secrets.
• Interaction mode: tasks/send, tasks/sendSubscribe, or tasks/get.
• Session behavior: new context/session or continue with a supplied contextId or sessionId.

Do not silently substitute a default CNAME. Present the recommended endpoints below as choices, accept a custom endpoint, or use a verified override such as OPAL_A2A_BASE_URL or OPAL_A2A_CNAME.

Recommended Endpoints

Offer these as non-exclusive choices when the user has not supplied a target:

1. https://netid-qa.openlinksw.com:8443
2. https://linkeddata.uriburner.com
3. https://demo.openlinksw.com

Also offer a custom base URL or full /chat/api/a2a endpoint. Do not assume the first endpoint is the default; wait for the user's selection or a verified config/env override.

Workflow

1. Normalize the target:
   • If the user gives a base URL, fetch the Agent Card from /.well-known/agent.json and derive the A2A endpoint from the card's url field.
   • If the user gives a full /chat/api/a2a URL, derive the Agent Card URL from the same origin unless the user supplies a separate card URL.
2. Fetch and inspect the Agent Card before sending tasks. Confirm name, provider, auth schemes, capabilities, input modes, output modes, and listed skills.
3. Authenticate:
   • For bearer/API key, send Authorization: Bearer {token}.
   • Prefer bearer tokens via --token-env, OPAL_A2A_TOKEN_ENV, or OPAL_A2A_TOKEN rather than raw --token.
   • For interactive OAuth, use dynamic client registration plus Authorization Code flow with --oauth-auth-code; register against the selected endpoint's own issuer, not a different host.
   • To reuse an OAuth-acquired bearer token, use --save-token-env OPAL_A2A_TOKEN --save-token-env-file .opal-a2a.env, then source the file in a shell you control.
   • For OAuth2 client credentials, use the card's token URL when present, or elicit an explicit token URL.
   • Never log tokens, client secrets, or complete Authorization headers.
4. Choose the task method:
   • Use tasks/send for a single request/response task.
   • Use tasks/sendSubscribe when the user asks for streaming or the card advertises streaming support and the user chooses it.
   • Use tasks/get to check an existing task ID.
5. Build JSON-RPC 2.0 payloads with text parts by default. Include attachments only from user-approved file paths.
6. Preserve returned task id, contextId, and sessionId values. Ask whether to continue the same context when the next request depends on prior task state.
7. Summarize results from status.message.parts, artifacts.parts, and final task state. Include IDs needed for follow-up, but keep secrets redacted.

Bundled Resources

• Read references/opal-a2a.md when you need protocol details, JSON-RPC payload examples, Agent Card field interpretation, or OPAL-specific behavior.
• Use scripts/a2a_client.py for repeatable command-line testing. Run python3 scripts/a2a_client.py --help before first use.

Validation

For skill changes, run:

python3 scripts/a2a_client.py --help

For live endpoint validation, use a user-approved target and credentials, then perform this minimum sequence:

python3 scripts/a2a_client.py card --agent-base https://{CNAME}
python3 scripts/a2a_client.py send --agent-base https://{CNAME} --token-env OPAL_A2A_TOKEN --message "What is Virtuoso?"
python3 scripts/a2a_client.py send --agent-base https://{CNAME} --oauth-auth-code --message "What is Virtuoso?"
python3 scripts/a2a_client.py send --agent-base https://{CNAME} --oauth-auth-code --save-token-env OPAL_A2A_TOKEN --save-token-env-file .opal-a2a.env --message "What is Virtuoso?"

Replace {CNAME} and token sources only with elicited values.