Mrthdrb

Previous example is correct. In addition... it's also possible by composer's config command.

composer.phar global config http-basic.repo.magento.com <public_key> <private_key>

Previous examples are correct. In addition it is also possible by composer's config command.

Inside the Magento project directory execute the following Composer command:

$ composer config http-basic.repo.magento.com <public_key> <private_key>

Just replace the placeholders with the actual values (public_key will become the username and private_key the password in HTTP authentication with repo.magento.com).

The auth settings can be tested by using fetching latest version with a faked update:

$ composer update --dry-run

This will give an error message like:

Invalid credentials for 'https://repo.magento.com/packages.json', aborting.

if something is wrong with the credentials.

I can strongly suggest to manage credentials inside the project folder as my answer suggests. I also would not edit the auth.json by hand but just with the composer command as it is less error-prone.

Login in magento using your credentials.
Then follow the navigation

1.My Account

2.Marketplace

3.My Access Key

4.Magento2

Public Key: xxxxx

Private Key:xxxxx

Public Key used as user name and Private Key used as password.

All answers are good just to compile possible scenarios on a single place.

Magento announced a new way to communicate to marketplace via compsoer, when you run composer install in the root directory of Magento it will prompt for username and password, remember this is not the Magento username and password it is Public and Private key of Magento Marketplace.

Login to Magento Marketplace.

Go to My Account.

Under My Products click Access Keys.

Select ver of Magento (1 or 2).

Click Create A New Access Key, in popup box name your key.

Clicking on Ok will generate pair of keys, Public and Private.

Now in Magento root or open ~/.composer/auth.json and put following lines

 "http-basic": 
 "repo.magento.com": 
 "username":"<your public key>",
 "password":"<your private key>"
 
 

You are good to go. Remember auth.json file contains standard json if you see any error just make sure that your auth file contains valid json, you can validate your json on JsonLint

If you don't want to add this information in above mentioned file (although it is handy, you don't need to open Marketplace dashboard repeatedly), then on run time just enter your Public key as username and Private key as your password, if you didn't add pair of keys in auth.json in previous step, don't worry Magento will ask you here whether to store this information or not, the choice is yours! :)

If this code will give error like auth.json does not contain valid JSON Parse error on line 1:

"http-basic": 
 "repo.magento.com": 
 "username":"<your public key>",
 "password":"<your private key>"
 

Than it will be like below:

 "http-basic": 
 "repo.magento.com": 
 "username":"<your public key>",
 "password":"<your private key>"
 
 

Here You should Wrap your auth.json File with extra

If you are trying from the command line interface :

Authentication required (repo.magento.com):

Username: "Your public key"

Password: "Your private key"

Remember here Username means "public key" and password means "private key"

Keep developing...

To Find Authentication username & password . Just follow below steps

Authentication required (repo.magento.com):
 Username: 

1. open https://marketplace.magento.com/customer/account/ & Login


2. Click on 'My Profile'


3. click 'Marketplace' Then Click 'My Access' link


4. On My Access Keys page, click on 'Magento 2' tab


5. click on 'Create A New Access Key' button, you will get two keys Public and Private: Public Key is your username; Private Key is your password


6. Copy key