diff --git a/CHANGELOG.md b/CHANGELOG.md
index c2c1d5769e..039bf2e597 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,8 @@
 
 - [fixed] Implemented a Node.js environment check that will be executed at
   package import time.
+- [fixed] Setting GOOGLE_APPLICATION_CREDENTIALS environment variable  
+  to a refresh token instead of a certificate token now supported
 
 # v6.5.0
 
diff --git a/src/auth/credential.ts b/src/auth/credential.ts
index e178ca8f10..fad788b7d3 100644
--- a/src/auth/credential.ts
+++ b/src/auth/credential.ts
@@ -356,8 +356,7 @@ export class ApplicationDefaultCredential implements Credential {
 
   constructor(httpAgent?: Agent) {
     if (process.env.GOOGLE_APPLICATION_CREDENTIALS) {
-      const serviceAccount = Certificate.fromPath(process.env.GOOGLE_APPLICATION_CREDENTIALS);
-      this.credential_ = new CertCredential(serviceAccount, httpAgent);
+      this.credential_ = credentialFromFile(process.env.GOOGLE_APPLICATION_CREDENTIALS, httpAgent);
       return;
     }
 
@@ -384,3 +383,49 @@ export class ApplicationDefaultCredential implements Credential {
     return this.credential_;
   }
 }
+
+function credentialFromFile(filePath: string, httpAgent?: Agent): Credential {
+  const credentialsFile = readCredentialFile(filePath);
+  if (typeof credentialsFile !== 'object') {
+    throw new FirebaseAppError(
+        AppErrorCodes.INVALID_CREDENTIAL,
+        'Failed to parse contents of the credentials file as an object',
+    );
+  }
+  if (credentialsFile.type === 'service_account') {
+    return new CertCredential(credentialsFile, httpAgent);
+  }
+  if (credentialsFile.type === 'authorized_user') {
+    return new RefreshTokenCredential(credentialsFile, httpAgent);
+  }
+  throw new FirebaseAppError(
+      AppErrorCodes.INVALID_CREDENTIAL,
+      'Invalid contents in the credentials file',
+  );
+}
+
+function readCredentialFile(filePath: string): {[key: string]: any} {
+  if (typeof filePath !== 'string') {
+    throw new FirebaseAppError(
+        AppErrorCodes.INVALID_CREDENTIAL,
+        'Failed to parse credentials file: TypeError: path must be a string',
+    );
+  }
+  let fileText: string;
+  try {
+    fileText = fs.readFileSync(filePath, 'utf8');
+  } catch (error) {
+    throw new FirebaseAppError(
+        AppErrorCodes.INVALID_CREDENTIAL,
+        `Failed to read credentials from file ${filePath}: ` + error,
+    );
+  }
+  try {
+    return JSON.parse(fileText);
+  } catch (error) {
+    throw new FirebaseAppError(
+        AppErrorCodes.INVALID_CREDENTIAL,
+        'Failed to parse contents of the credentials file as an object: ' + error,
+    );
+  }
+}
diff --git a/test/unit/auth/credential.spec.ts b/test/unit/auth/credential.spec.ts
index 27fdf7cb48..e902f65da2 100644
--- a/test/unit/auth/credential.spec.ts
+++ b/test/unit/auth/credential.spec.ts
@@ -31,8 +31,8 @@ import * as utils from '../utils';
 import * as mocks from '../../resources/mocks';
 
 import {
-  ApplicationDefaultCredential, CertCredential, Certificate, GoogleOAuthAccessToken,
-  MetadataServiceCredential, RefreshTokenCredential,
+  ApplicationDefaultCredential, CertCredential, Certificate, Credential, GoogleOAuthAccessToken,
+  MetadataServiceCredential, RefreshToken, RefreshTokenCredential,
 } from '../../../src/auth/credential';
 import { HttpClient } from '../../../src/utils/api-request';
 import {Agent} from 'https';
@@ -337,7 +337,7 @@ describe('Credential', () => {
       if (fsStub) {
         fsStub.restore();
       }
-      process.env.GOOGLE_APPLICATION_CREDENTIALS = this.credPath;
+      process.env.GOOGLE_APPLICATION_CREDENTIALS = credPath;
     });
 
     it('should return a CertCredential with GOOGLE_APPLICATION_CREDENTIALS set', () => {
@@ -356,6 +356,19 @@ describe('Credential', () => {
       expect(() => new ApplicationDefaultCredential()).to.throw(Error);
     });
 
+    it('should throw error if type not specified on cert file', () => {
+      fsStub = sinon.stub(fs, 'readFileSync').returns(JSON.stringify({}));
+      expect(() => new ApplicationDefaultCredential())
+          .to.throw(Error, 'Invalid contents in the credentials file');
+    });
+
+    it('should throw error if type is unknown on cert file', () => {
+      fsStub = sinon.stub(fs, 'readFileSync').returns(JSON.stringify({
+        type: 'foo',
+      }));
+      expect(() => new ApplicationDefaultCredential()).to.throw(Error, 'Invalid contents in the credentials file');
+    });
+
     it('should return a RefreshTokenCredential with gcloud login', () => {
       if (skipAndLogWarningIfNoGcloud()) {
         return;
@@ -395,6 +408,24 @@ describe('Credential', () => {
         privateKey: mockCertificateObject.private_key,
       });
     });
+
+    it('should parse valid RefreshTokenCredential if GOOGLE_APPLICATION_CREDENTIALS environment variable ' +
+        'points to default refresh token location', () => {
+      process.env.GOOGLE_APPLICATION_CREDENTIALS = GCLOUD_CREDENTIAL_PATH;
+
+      fsStub = sinon.stub(fs, 'readFileSync').returns(JSON.stringify(MOCK_REFRESH_TOKEN_CONFIG));
+
+      const adc = new ApplicationDefaultCredential();
+      const c = adc.getCredential();
+      expect(c).is.instanceOf(RefreshTokenCredential);
+      expect(c).to.have.property('refreshToken').that.includes({
+        clientId: MOCK_REFRESH_TOKEN_CONFIG.client_id,
+        clientSecret: MOCK_REFRESH_TOKEN_CONFIG.client_secret,
+        refreshToken: MOCK_REFRESH_TOKEN_CONFIG.refresh_token,
+        type: MOCK_REFRESH_TOKEN_CONFIG.type,
+      });
+      expect(fsStub.alwaysCalledWith(GCLOUD_CREDENTIAL_PATH, 'utf8')).to.be.true;
+    });
   });
 
   describe('HTTP Agent', () => {