Add WebCrypto detection for crypto components (#16)

* Add WebCrypto detection for crypto components

* Fix typos in tests

Author: jeskew

packages/crypto-supports-webCrypto/.gitignore

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+node_modules
+*.js
+*.js.map
+*.d.ts

packages/crypto-supports-webCrypto/__tests__/supportsWebCrypto.ts

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+import {supportsWebCrypto} from "../lib/supportsWebCrypto";
+
+const fakeWindow: Window = {
+    crypto: {
+        getRandomValues: () => {},
+        subtle: {
+            decrypt(alg: any, key: any) { return {} as any; },
+            digest(alg: any) { return {} as any; },
+            encrypt(alg: any, key: any) { return {} as any; },
+            exportKey(format: any, key: any) { return {} as any; },
+            generateKey(alg: any) { return {} as any; },
+            importKey(format: any, keyData: any, alg: any) { return {} as any; },
+            sign(alg: any, key: any) { return {} as any; },
+            verify(alg: any, key: any, signature: any) { return {} as any; },
+        },
+    },
+} as any;
+
+describe('supportsWebCrypto', () => {
+    it(
+        'should return false if an object does not fulfill the WebCrypto interface',
+        () => {
+            expect(supportsWebCrypto({} as any)).toBe(false);
+        }
+    );
+
+    it(
+        'should return true if an object fulfills the WebCrypto interface',
+        () => {
+            expect(supportsWebCrypto(fakeWindow)).toBe(true);
+        }
+    );
+});

packages/crypto-supports-webCrypto/index.ts

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+export * from './lib/supportsWebCrypto';

packages/crypto-supports-webCrypto/lib/supportsWebCrypto.ts

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+type SubtleCryptoMethod = 'decrypt'|'digest'|'encrypt'|'exportKey'|'generateKey'|'importKey'|'sign'|'verify';
+
+const subtleCryptoMethods: Array<SubtleCryptoMethod> = [
+    'decrypt',
+    'digest',
+    'encrypt',
+    'exportKey',
+    'generateKey',
+    'importKey',
+    'sign',
+    'verify',
+];
+
+export function supportsWebCrypto(window: Window): boolean {
+    if (
+        typeof window === 'object' &&
+        typeof window.crypto === 'object' &&
+        typeof window.crypto.subtle === 'object'
+    ) {
+        const {getRandomValues, subtle} = window.crypto;
+        const methodsToTest = subtleCryptoMethods
+            .map<Function>(methodName => subtle[methodName])
+            .concat(getRandomValues);
+
+        for (let method of methodsToTest) {
+            if (typeof method !== 'function') {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    return false;
+}

packages/crypto-supports-webCrypto/package.json

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+{
+  "name": "@aws/crypto-supports-webCrypto",
+  "private": true,
+  "version": "0.0.1",
+  "description": "Provides functions for detecting if the host environment supports the WebCrypto API",
+  "scripts": {
+    "pretest": "tsc",
+    "test": "jest"
+  },
+  "author": "[email protected]",
+  "license": "UNLICENSED",
+  "main": "index.js",
+  "devDependencies": {
+    "@types/jest": "^19.2.2",
+    "jest": "^19.0.2",
+    "typescript": "^2.3"
+  }
+}

packages/crypto-supports-webCrypto/tsconfig.json

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+{
+    "compilerOptions": {
+        "module": "commonjs",
+        "target": "es5",
+        "strict": true,
+        "sourceMap": true,
+        "declaration": true
+    }
+}