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There is no universal MCP setting for an API key header. Find the configuration fields supported by your exact client and connection type, then supply credentials in the format the remote server expects. For example, OpenAI’s Agents API HTTP transport documents authorization and headers, while Anthropic’s MCP connector uses an authorization_token field for an OAuth authorization token. Those fields are not interchangeable.
First identify the client, connection type, and authentication scheme
Before editing a configuration, check three things: which MCP client or API you are using, where the HTTP connection originates, and what credential format the server accepts. A server might require a bearer token in Authorization, a raw API key, or a vendor-specific header such as X-API-Key. One format is not automatically equivalent to another.
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OpenAI’s Agents API distinguishes HTTP connections made from OpenAI, HTTP connections made from an execution environment, and stdio connections. The supported way to provide credentials depends on that connection origin. See OpenAI’s remote MCP connection guide. For services documented by Google Cloud, authentication may use bearer tokens or API keys in the Authorization header, but that guidance is specific to those services; follow the instructions for your MCP server. See Google Cloud’s API key authentication documentation.
Configure an HTTP transport in the OpenAI Agents API
For an OpenAI Agents API HTTP MCP connection, the documented transport can include an authorization value and additional headers. The following illustrates the field names and shape; replace the example URL, token, and tenant value with ones appropriate to your server.
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{
"type": "http",
"server_url": "https://mcp.example.com/mcp",
"authorization": "Bearer YOUR_MCP_ACCESS_TOKEN",
"headers": { "X-Tenant-ID": "tenant_123" }
}Use the scheme the server requires. If it expects a raw API key or a different header, do not assume that placing a bearer token in authorization will work; configure the value and header according to both sides’ documentation.
OpenAI documents inline credentials and matching vault credentials as alternative sources for Authorization. Use one source, not both. Vault-backed MCP authentication applies to connections from OpenAI; for HTTP connections originating in an execution environment, the guide describes inline authentication or a trusted proxy.
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Use the correct credential field in other clients
Anthropic Messages API MCP connector
Anthropic’s Messages API connector documents a server definition with type: "url", a server URL, a name, and authorization_token. The field is described for an OAuth authorization token—not as a universal slot for any API key. API consumers obtain the access token before the request and refresh it as needed. The feature is labeled beta in the documentation, so check the current Anthropic MCP connector guide for its present requirements.
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Codex’s MCP configuration documentation describes an optional http_headers_helper that prints a JSON object of header names and string values. Explicit bearer tokens and OAuth credentials take precedence over an Authorization header supplied by the helper. Consult the Codex MCP configuration documentation for the supported configuration details.
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Keep credentials out of reusable or exposed configuration
Treat API keys, bearer tokens, and OAuth credentials as secrets. OpenAI advises keeping secrets out of reusable agent definitions, plugin archives, and logs. If agent-generated code must not be able to access credentials, OpenAI recommends supplying them outside the environment through a trusted proxy or server.
- Do not commit live credentials to shared configuration or source control.
- Avoid logging authorization values or including them in error reports.
- For OpenAI’s documented vault-backed setup, do not also provide a second Authorization source inline.
- For OAuth, account for token acquisition and refresh instead of assuming a static key will remain valid.
Troubleshoot a remote MCP connection that fails
- Check the URL. Confirm that the server URL is correct and points to the expected MCP endpoint.
- Check connection origin and reachability. Determine whether the connection comes from the client service or an execution environment. If it originates in an environment, confirm that the executor can reach the server.
- Check the credential format. Verify whether the server requires a bearer token, an API key, OAuth, or a vendor-specific header, and match the header name and value exactly.
- Check for duplicate Authorization sources. In OpenAI’s Agents API configuration, use inline configuration or a matching vault credential as the Authorization source, not both.
- Inspect initialization errors. If a required server does not initialize, review the client’s initialization errors as recommended in OpenAI’s guide; they can help distinguish a connection problem from an authentication mismatch.
What to compare before choosing a setup
When evaluating a client configuration, compare the client and version, connection origin, accepted credential type, how headers are injected, and where secrets are stored or refreshed. The documented examples from OpenAI, Anthropic, and Google Cloud describe different integrations; they are not a compatibility matrix for every MCP client.
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