feat(core): resolve auth schemes based on the preference list

.changeset/fluffy-ducks-grin.md

@@ -0,0 +1,5 @@
+---
+"@smithy/core": minor
+---
+
+Resolve auth schemes based on the preference list

packages/core/src/middleware-http-auth-scheme/httpAuthSchemeMiddleware.ts

@@ -6,6 +6,7 @@ import {
   HttpAuthSchemeParametersProvider,
   HttpAuthSchemeProvider,
   IdentityProviderConfig,
+  Provider,
   SelectedHttpAuthScheme,
   SerializeHandler,
   SerializeHandlerArguments,
@@ -15,10 +16,13 @@ import {
 } from "@smithy/types";
 import { getSmithyContext } from "@smithy/util-middleware";
 
+import { resolveAuthOptions } from "./resolveAuthOptions";
+
 /**
  * @internal
  */
 export interface PreviouslyResolved<TParameters extends HttpAuthSchemeParameters> {
+  authSchemePreference?: Provider<string[]>;
   httpAuthSchemes: HttpAuthScheme[];
   httpAuthSchemeProvider: HttpAuthSchemeProvider<TParameters>;
 }
@@ -84,10 +88,14 @@ export const httpAuthSchemeMiddleware =
     const options = config.httpAuthSchemeProvider(
       await mwOptions.httpAuthSchemeParametersProvider(config, context as TContext, args.input)
     );
+
+    const authSchemePreference = config.authSchemePreference ? await config.authSchemePreference() : [];
+    const resolvedOptions = resolveAuthOptions(options, authSchemePreference);
+
     const authSchemes = convertHttpAuthSchemesToMap(config.httpAuthSchemes);
     const smithyContext: HttpAuthSchemeMiddlewareSmithyContext = getSmithyContext(context);
     const failureReasons = [];
-    for (const option of options) {
+    for (const option of resolvedOptions) {
       const scheme = authSchemes.get(option.schemeId);
       if (!scheme) {
         failureReasons.push(`HttpAuthScheme \`${option.schemeId}\` was not enabled for this service.`);

packages/core/src/middleware-http-auth-scheme/resolveAuthOptions.spec.ts

@@ -0,0 +1,42 @@
+import { HttpAuthOption } from "@smithy/types";
+import { describe, expect, it } from "vitest";
+
+import { resolveAuthOptions } from "./resolveAuthOptions";
+
+describe("resolveAuthSchemes", () => {
+  const sigv4 = "sigv4";
+  const sigv4a = "sigv4a";
+
+  const mockSigV4AuthScheme = { schemeId: `aws.auth#${sigv4}` } as HttpAuthOption;
+  const mockSigV4aAuthScheme = { schemeId: `aws.auth#${sigv4a}` } as HttpAuthOption;
+
+  it("should return candidate auth schemes is preference list is not available", () => {
+    const candidateAuthSchemes = [mockSigV4AuthScheme, mockSigV4aAuthScheme];
+    expect(resolveAuthOptions(candidateAuthSchemes, [])).toEqual(candidateAuthSchemes);
+
+    // @ts-expect-error case where callee incorrectly passes undefined
+    expect(resolveAuthOptions(candidateAuthSchemes)).toEqual(candidateAuthSchemes);
+  });
+
+  it("should return auth scheme from preference if it's available", () => {
+    expect(resolveAuthOptions([mockSigV4AuthScheme, mockSigV4aAuthScheme], [sigv4a])).toEqual([
+      mockSigV4aAuthScheme,
+      mockSigV4AuthScheme,
+    ]);
+
+    expect(resolveAuthOptions([mockSigV4AuthScheme, mockSigV4aAuthScheme], [sigv4a, sigv4])).toEqual([
+      mockSigV4aAuthScheme,
+      mockSigV4AuthScheme,
+    ]);
+
+    expect(resolveAuthOptions([mockSigV4AuthScheme, mockSigV4aAuthScheme], [sigv4, sigv4a])).toEqual([
+      mockSigV4AuthScheme,
+      mockSigV4aAuthScheme,
+    ]);
+  });
+
+  it("should ignore auth scheme from preference if it's not available", () => {
+    expect(resolveAuthOptions([mockSigV4AuthScheme], [sigv4a])).toEqual([mockSigV4AuthScheme]);
+    expect(resolveAuthOptions([mockSigV4AuthScheme], ["sigv3"])).toEqual([mockSigV4AuthScheme]);
+  });
+});

packages/core/src/middleware-http-auth-scheme/resolveAuthOptions.ts

@@ -0,0 +1,39 @@
+import { HttpAuthOption } from "@smithy/types";
+
+/**
+ * Resolves list of auth options based on the supported ones, vs the preference list.
+ *
+ * @param candidateAuthOptions list of supported auth options selected by the standard
+ *   resolution process (model-based, endpoints 2.0, etc.)
+ * @param authSchemePreference list of auth schemes preferred by user.
+ * @returns
+ */
+export const resolveAuthOptions = (
+  candidateAuthOptions: HttpAuthOption[],
+  authSchemePreference: string[]
+): HttpAuthOption[] => {
+  if (!authSchemePreference || authSchemePreference.length === 0) {
+    return candidateAuthOptions;
+  }
+
+  // reprioritize candidates based on user's preference
+  const preferredAuthOptions = [];
+
+  for (const preferredSchemeName of authSchemePreference) {
+    for (const candidateAuthOption of candidateAuthOptions) {
+      const candidateAuthSchemeName = candidateAuthOption.schemeId.split("#")[1];
+      if (candidateAuthSchemeName === preferredSchemeName) {
+        preferredAuthOptions.push(candidateAuthOption);
+      }
+    }
+  }
+
+  // add any remaining candidates that weren't in the preference list
+  for (const candidateAuthOption of candidateAuthOptions) {
+    if (!preferredAuthOptions.find(({ schemeId }) => schemeId === candidateAuthOption.schemeId)) {
+      preferredAuthOptions.push(candidateAuthOption);
+    }
+  }
+
+  return preferredAuthOptions;
+};