Accessing Key Vault with @azure/identity and get error 'Request is missing a Bearer or PoP token Error 401'

I'm trying to retrieve some secrets from Azure's keyvault but I cannot seem to authenticate using @azure/identity module.

Versions:

"@azure/identity": "^1.0.0-preview.6",
"@azure/keyvault-secrets": "^4.0.0-preview.9",

I have an azure functions app and I have configured the app both in production and locally using the local.settings.json having filled in the proper values for:

{
    "IsEncrypted": false,
    "Values": {
        "AZURE_CLIENT_ID": "REDACTED",
        "AZURE_CLIENT_SECRET": "REDACTED",
        "AZIRE_TENANT_ID": "REDACTED"
    },
    "ConnectionStrings": {}
}

• App Registered via Azure Active Directory => App Registrations.
• Disabled login
• Created App Secret

Then, I have added the app to the keyvault with the role 'reader' giving it the ability to 'get' secrets but nothing else, not even list:

Now when I try to retreive the secrets:

import { KeyVaultSecret, SecretClient } from '@azure/keyvault-secrets';
import { EnvironmentCredential } from '@azure/identity';

export const GetSecret = async (key: string): Promise<string> => {
    try {
        const credential: EnvironmentCredential = new EnvironmentCredential();

        console.log('CREDENTIAL: ', credential);
        console.log('CLIENT SECRET', process.env.AZURE_CLIENT_SECRET);
        console.log('CLIENT ID', process.env.AZURE_CLIENT_ID);

        const url = 'https://tlabs-vault.vault.azure.net';
        const client = new SecretClient(url, credential);
        let secret: KeyVaultSecret = await client.getSecret(key);
        return secret.value;
    } catch (err) {
        console.error('Error getting secret from Azure Vault', err);
    }
};

But this is not working, on the console I see the result of credentials as:

EnvironmentCredential { _credential: undefined }

And the full request that throws the error:

request:
[10/28/2019 1:14:16 PM]    WebResource {
[10/28/2019 1:14:16 PM]      streamResponseBody: false,
[10/28/2019 1:14:16 PM]      url:
[10/28/2019 1:14:16 PM]       'https://REDACTED_VAULT_NAME.vault.azure.net/secrets/REDACTED_SECRET_NAME/?api-version=7.0',
[10/28/2019 1:14:16 PM]      method: 'GET',
[10/28/2019 1:14:16 PM]      headers: HttpHeaders { _headersMap: [Object] },
[10/28/2019 1:14:16 PM]      body: undefined,
[10/28/2019 1:14:16 PM]      query: undefined,
[10/28/2019 1:14:16 PM]      formData: undefined,
[10/28/2019 1:14:16 PM]      withCredentials: false,
[10/28/2019 1:14:16 PM]      abortSignal: undefined,
[10/28/2019 1:14:16 PM]      timeout: 0,
[10/28/2019 1:14:16 PM]      onUploadProgress: undefined,
[10/28/2019 1:14:16 PM]      onDownloadProgress: undefined,
[10/28/2019 1:14:16 PM]      proxySettings: undefined,
[10/28/2019 1:14:16 PM]      keepAlive: true,
[10/28/2019 1:14:16 PM]      operationSpec:
[10/28/2019 1:14:16 PM]       { httpMethod: 'GET',
[10/28/2019 1:14:16 PM]         path: 'secrets/{secret-name}/{secret-version}',
[10/28/2019 1:14:16 PM]         urlParameters: [Array],
[10/28/2019 1:14:16 PM]         queryParameters: [Array],
[10/28/2019 1:14:16 PM]         responses: [Object],
[10/28/2019 1:14:16 PM]         serializer: [Serializer] } },
[10/28/2019 1:14:16 PM]   response:
[10/28/2019 1:14:16 PM]    { body:
[10/28/2019 1:14:16 PM]       '{"error":{"code":"Unauthorized","message":"Request is missing a Bearer or PoP token."}}',
[10/28/2019 1:14:16 PM]      headers: HttpHeaders { _headersMap: [Object] },
[10/28/2019 1:14:16 PM]      status: 401,
[10/28/2019 1:14:16 PM]      parsedBody: { error: [Object] } },
[10/28/2019 1:14:16 PM]   details:
[10/28/2019 1:14:16 PM]    { error:
[10/28/2019 1:14:16 PM]       { code: 'Unauthorized',
[10/28/2019 1:14:16 PM]         message: 'Request is missing a Bearer or PoP token.' } } }