A2A Host

Feature Name	Agent to Agent Protocol (A2A) Host
Feature ID	CrestApps.OrchardCore.AI.A2A.Host

The A2A Host feature exposes all AI Profiles of type Agent as discoverable agents via the Agent-to-Agent protocol. External A2A clients can discover available agents and send messages to them.

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Agent Exposure Modes

The A2A Host supports two modes for how agents are exposed:

Multi-Agent Mode (Default)

Each Agent AI Profile is exposed as its own independent agent card. The /.well-known/agent-card.json endpoint returns a JSON array of agent cards. Each card has its own url property pointing to /a2a?agent={agentName}.

Skill Mode

When ExposeAgentsAsSkill is enabled, a single combined agent card is returned. All Agent AI Profiles are listed as skills within that card. Messages are routed using the agentName metadata field.

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Endpoints

When the A2A Host feature is enabled, the following endpoints become available:

Endpoint	Description
/.well-known/agent-card.json	Returns agent card(s) for discovery (array in multi-agent mode, single object in skill mode)
/a2a	The A2A JSON-RPC endpoint for sending messages to agents
/a2a?agent={name}	Routes to a specific agent in multi-agent mode

Sending Messages

Messages sent to /a2a are routed to the appropriate agent based on:

1. Query parameter routing (multi-agent mode): The ?agent={name} query parameter specifies the target agent.
2. Metadata routing: If the message includes agentName in its metadata, it routes to that specific agent.
3. Default routing: If no agent is specified, the message is routed to the first available agent.

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Authentication

The A2A Host supports the same authentication patterns as the MCP Server:

Authentication Type	Description
None	No authentication required. Suitable for development environments.
API Key	Clients must provide an API key for access.
OpenId	Clients authenticate using OpenID Connect tokens. Enable the OrchardCore OpenIddict server feature for automatic integration.

Configuration

Authentication is configured via shell configuration (e.g., appsettings.json):

{
  "OrchardCore": {
    "CrestApps_AI": {
      "A2AHost": {
        "AuthenticationType": "None",
        "ApiKey": "your-api-key-here",
        "RequireAccessPermission": false,
        "ExposeAgentsAsSkill": false
      }
    }
  }
}

Setting	Type	Default	Description
AuthenticationType	None | ApiKey | OpenId	OpenId	The authentication method for the A2A endpoint
ApiKey	string		The API key value (required when using ApiKey authentication)
RequireAccessPermission	bool	true	When true, authenticated users must also have the AccessA2AHost permission
ExposeAgentsAsSkill	bool	false	When true, all agents are combined into a single card with skills instead of individual cards

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Permissions

Permission	Description
Access A2A Host	Required when RequireAccessPermission is enabled in host options