Legacy Mojang Authentication

Minecraft 1.6 introduced a new authentication scheme called Yggdrasil which completely replaces the previous authentication system.

Request format

All requests to Yggdrasil are made to the following server:

 https://authserver.mojang.com

Further, they are expected to fulfill the following rules:

• Are POST requests
• Have the Content-Type header set to application/json
• Contain a JSON-encoded dictionary as payload

If a request was successful the server will respond with:

• Status code 200
• A JSON-encoded dictionary according to the specifications below

If however a request fails, the server will respond with:

• An appropriate, non-200 HTTP status code
• A JSON-encoded dictionary following this format:

<syntaxhighlight lang="javascript"> {

 "error": "Short description of the error",
 "errorMessage": "Longer description which can be shown to the user",
 "cause": "Cause of the error"        // optional

} </syntaxhighlight>

Errors

These are some of the errors that can be encountered:

Error	Cause	Error message	Notes
Method Not Allowed		The method specified in the request is not allowed for the resource identified by the request URI	Something other than a POST request was received.
Not Found		The server has not found anything matching the request URI	Non-existing endpoint was called.
ForbiddenOperationException	UserMigratedException	Invalid credentials. Account migrated, use e-mail as username.
ForbiddenOperationException		Invalid credentials. Invalid username or password.
ForbiddenOperationException		Invalid token.	accessToken was invalid.
IllegalArgumentException		Access token already has a profile assigned.	Selecting profiles isn't implemented yet.

Session ID

Whenever a Mojang service requires a session ID, you can simply combine a valid accessToken with the corresponding profile identifier as follows:

 token:<accessToken>:<profile ID>

Authenticate

Authenticates a user using his password.

Endpoint

 /authenticate

Payload

<syntaxhighlight lang="javascript"> {

 "agent": {                             // optional
   "name": "Minecraft",                 // So far this is the only encountered value
   "version": 1                         // This number might be increased
                                        // by the vanilla client in the future
 },
 "username": "mojang account name",     // Can be an email address or player name for
                                        // unmigrated accounts
 "password": "mojang account password",
 "clientToken": "client identifier"     // optional

} </syntaxhighlight>

The clientToken should be a randomly generated identifier and must be identical for each request. In case it is omitted the server will generate a random token based on Java's UUID.toString() which should then be stored by the client. This will however also invalidate all previously acquired accessTokens for this user across all clients.

Response

<syntaxhighlight lang="javascript"> {

 "accessToken": "random access token",  // hexadecimal
 "clientToken": "client identifier",    // identical to the one received
 "availableProfiles": [                 // only present if the agent field was received
   {
     "id": "profile identifier",        // hexadecimal
     "name": "player name"
   }
 ],
 "selectedProfile": {                   // only present if the agent field was received
   "id": "profile identifier",
   "name": "player name"
 }

} </syntaxhighlight> Note: If a user wishes to stay logged in on his computer you are strongly advised to store the received accessToken instead of the password itself.

Currently each account will only have one single profile, multiple profiles per account are however planned in the future.

Refresh

Refreshes a valid accessToken. It can be uses to keep a user logged in between gaming sessions and is preferred over storing the user's password in a file (see lastlogin).

Endpoint

 /refresh

Payload

<syntaxhighlight lang="javascript"> {

 "accessToken": "valid accessToken",
 "clientToken": "client identifier"     // This needs to be identical to the one used
                                        // to obtain the accessToken in the first place
 "selectedProfile": {                   // optional; sending it will result in an error
   "id": "profile identifier",          // hexadecimal
   "name": "player name"
 }

} </syntaxhighlight>

Note: The provided accessToken gets invalidated.

Response

<syntaxhighlight lang="javascript"> {

 "accessToken": "random access token",  // hexadecimal
 "clientToken": "client identifier",    // identical to the one received
 "selectedProfile": {
   "id": "profile identifier",          // hexadecimal
   "name": "player name"
 }

} </syntaxhighlight>

Validate

Checks if an accessToken is valid.

Endpoint

 /validate

Payload

<syntaxhighlight lang="javascript"> {

 "accessToken": "valid accessToken",

} </syntaxhighlight>

Response

Unlike most other methods this one will return an empty payload if successful.

Joining a Server

See Protocol Encryption