<p>When deploying AI agents with <span class="LinkEnhancement"><a class="Link" href="https://aws.amazon.com/bedrock/agentcore/" target="_blank" rel="noopener" data-cms-ai="0">Amazon Bedrock AgentCore</a></span>, organizations benefit from built-in modern support for OAuth 2.0, <span class="LinkEnhancement"><a class="Link" href="https://aws.amazon.com/iam/" target="_blank" rel="noopener" data-cms-ai="0">AWS Identity and Access Management (IAM)</a></span>, and API key authentication through <span class="LinkEnhancement"><a class="Link" href="https://aws.amazon.com/blogs/machine-learning/introducing-amazon-bedrock-agentcore-gateway-transforming-enterprise-ai-agent-tool-development/" target="_blank" rel="noopener" data-cms-ai="0">Amazon Bedrock AgentCore Gateway</a></span>. However, some enterprise environments still use legacy authentication mechanisms such as HTTP Basic Authentication (Basic Auth) (<span class="LinkEnhancement"><a class="Link" href="https://datatracker.ietf.org/doc/html/rfc7617" target="_blank" rel="noopener" data-cms-ai="0">RFC 7617)</a></span>. The extensible architecture of AgentCore Gateway enables support for these authentication mechanisms through a <span class="LinkEnhancement"><a class="Link" href="https://docs.aws.amazon.com/bedrock-agentcore/latest/devguide/gateway-interceptors.html" target="_blank" rel="noopener" data-cms-ai="0">request Lambda interceptor</a></span>—custom code that runs each time an agent calls a tool.</p>
<p>In this post, we show you how to use a request Lambda interceptor to authenticate to a downstream tool API using system credentials, retrieving a service account credential from <span class="LinkEnhancement"><a class="Link" href="https://aws.amazon.com/secrets-manager/" target="_blank" rel="noopener" data-cms-ai="0">AWS Secrets Manager</a></span> and constructing a Basic Auth header. This design keeps credentials isolated from the agent, designed to mitigate exposure through model-driven behavior such as prompt injection.</p>
<blockquote>
<p><b>Important</b>: Basic Auth is an antiquated technology that transmits credentials as Base64-encoded text and should not be used as a long-term authentication strategy. AWS recommends modernizing to OAuth 2.0, SAML, OpenID Connect, or IAM where possible. However, some organizations with legacy workloads choose to decouple authentication modernization from their agentic AI adoption, addressing each on independent timelines. If your environment requires Basic Auth integration as an interim measure, consult your AWS Solutions Architect to evaluate the security trade-offs before proceeding. We’re providing this post as a reusable implementation, but it shouldn’t be construed as an endorsement of Basic Auth, or considered suitable as a long-term solution.</p>
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<h2>Solution overview</h2>
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<p>The solution uses a request Lambda interceptor in AgentCore Gateway to retrieve system credentials and construct a Basic Auth header for the downstream tool API. Figure 1 shows the end-to-end flow.</p>
<div id="attachment_43371" style="width: 1012px" class="wp-caption aligncenter">
<img aria-describedby="caption-attachment-43371" loading="lazy" src="https://d2908q01vomqb2.cloudfront.net/22d200f8670dbdb3e253a90eee5098477c95c23d/2026/08/17/image1-1.png" alt="Figure 1: Solution workflow" width="1002" height="748" class="size-full wp-image-43371">
<p id="caption-attachment-43371" class="wp-caption-text">Figure 1: Solution workflow</p>
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<ol id="rte-3c0dfe00-91c9-11f1-b01e-4f9b3f5fd40a" class="rte2-style-ol" start="1">
<li>The AI agent initiates a tool call over Model Context Protocol (MCP) to the gateway with an inbound JSON Web Token (JWT) issued by a configured identity provider (IdP). The MCP request body contains the tool name and any required parameters. The gateway’s inbound authentication layer validates the token against the IdP specified in the inbound authorizer configuration.</li>
<li>After inbound authentication succeeds, the gateway invokes the request Lambda interceptor, passing the original request payload and headers, including the validated JWT and its embedded claims.</li>
<li>The request Lambda interceptor re-validates the inbound JWT issued by the configured IdP as a defense-in-depth measure, then retrieves the system service account credential from Secrets Manager. The credential is a service account that authenticates the AI agent to the downstream tool.</li>
<li>The interceptor then constructs a compliant Basic Auth header using the system credential and adds it to the outbound request. Because Basic Auth transmits credentials as Base64