chore(credential-providers): unavailable browser credential providers throw at runtime

packages/credential-providers/README.md

@@ -505,7 +505,8 @@ See [`fromSSO()`](#fromsso) fro more information
 
 ## `fromEnv()`
 
-- Not available in browser & native apps
+- Not available in browser & native apps unless your code or bundler populates the
+  `process.env` global object.
 
 ```javascript
 import { fromEnv } from "@aws-sdk/credential-providers"; // ES6 import

packages/credential-providers/src/fromEnv.ts

@@ -24,5 +24,8 @@ import { AwsCredentialIdentityProvider } from "@smithy/types";
  *   credentials: fromEnv(),
  * });
  * ```
+ *
+ * To use this in non-Node.js environments such as a browser, your code or
+ * build system must populate the `process.env` global object.
  */
 export const fromEnv = (init?: FromEnvInit): AwsCredentialIdentityProvider => _fromEnv(init);

packages/credential-providers/src/index.browser.ts

@@ -2,5 +2,6 @@ export * from "./fromCognitoIdentity";
 export * from "./fromCognitoIdentityPool";
 export { fromHttp } from "@aws-sdk/credential-provider-http";
 export type { FromHttpOptions, HttpProviderCredentials } from "@aws-sdk/credential-provider-http";
+export * from "./fromEnv";
 export * from "./fromTemporaryCredentials";
 export * from "./fromWebToken";