Social.localUser.userName == "Lerpz"

Following the instructions on the Play Game Services page (GitHub - playgameservices/play-games-plugin-for-unity: Google Play Games plugin for Unity), I always get a user named Lerpz after authenticating. How do I authenticate a legitimate user instead of the default?

I/Unity   (32711): Success: True
I/Unity   (32711): UnityEngine.Debug:Internal_Log(Int32, String, Object)
I/Unity   (32711): UnityEngine.Debug:Log(Object)
I/Unity   (32711): ShowLeaderboard:<OnShowLeaderboard>m__112(Boolean) (at /Users/MaskedPixel/Development/Unity/weeklys/Week05/Assets/GreatWhiteFlight/Scripts/Util/UI/ShowLeaderboard.cs:12)
I/Unity   (32711): UnityEngine.SocialPlatforms.Local:UnityEngine.SocialPlatforms.ISocialPlatform.Authenticate(ILocalUser, Action`1)
I/Unity   (32711): UnityEngine.SocialPlatforms.Impl.LocalUser:Authenticate(Action`1)
I/Unity   (32711): ShowLeaderboard:OnShowLeaderboard() (at /Users/MaskedPixel/Development/Unity/weeklys/Week05/Assets/GreatWhiteFlight/Scripts/Util/UI/ShowLeaderboard.cs:11)
I/Unity   (32711): UnityEngine.Events.InvokableCall:Invoke(Object[])
I/Unity   (32711): UnityEngine.Events.InvokableCallList:Invoke(Object[])
I/Unity   (32711): UnityEngine.Events.UnityEventBase:Invoke(Object[])
I/Unity   (32711): UnityEngine.Events.UnityEvent:Invoke()
I/Unity   (32711): UnityEngine.UI.Button:Press() (at /Users/builduser/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/UI/Core/Button.cs:35)
I/Unity   (32711): UnityEngine.UI.Button:OnPointerClick(PointerEventData) (at /Users/builduser/buildslave/unity/bu
I/Unity   (32711): Username: Lerpz
I/Unity   (32711): UnityEngine.Debug:Internal_Log(Int32, String, Object)
I/Unity   (32711): UnityEngine.Debug:Log(Object)
I/Unity   (32711): ShowLeaderboard:<OnShowLeaderboard>m__112(Boolean) (at /Users/MaskedPixel/Development/Unity/weeklys/Week05/Assets/GreatWhiteFlight/Scripts/Util/UI/ShowLeaderboard.cs:13)
I/Unity   (32711): UnityEngine.SocialPlatforms.Local:UnityEngine.SocialPlatforms.ISocialPlatform.Authenticate(ILocalUser, Action`1)
I/Unity   (32711): UnityEngine.SocialPlatforms.Impl.LocalUser:Authenticate(Action`1)
I/Unity   (32711): ShowLeaderboard:OnShowLeaderboard() (at /Users/MaskedPixel/Development/Unity/weeklys/Week05/Assets/GreatWhiteFlight/Scripts/Util/UI/ShowLeaderboard.cs:11)
I/Unity   (32711): UnityEngine.Events.InvokableCall:Invoke(Object[])
I/Unity   (32711): UnityEngine.Events.InvokableCallList:Invoke(Object[])
I/Unity   (32711): UnityEngine.Events.UnityEventBase:Invoke(Object[])
I/Unity   (32711): UnityEngine.Events.UnityEvent:Invoke()
I/Unity   (32711): UnityEngine.UI.Button:Press() (at /Users/builduser/buildslave/unity/build/Extensions/guisystem/UnityEngine.UI/UI/Core/Button.cs:35)
I/Unity   (32711): UnityEngine.UI.Button:OnPointerClick(PointerEventData) (at /Users/builduser/buildslave/unity/

You need to activate the Google Play Platform with

PlayGamesPlatform.Activate(); //Call it in Start() or Awake()

https://gamedevelopmentadventures.wordpress.com/2015/04/06/publishing-an-android-game-with-unity-and-adding-google-game-services/