[Nexus 6  General] joyrida12:
So I fell victim to googles new FRP Security feature that requires you to log in using the same gmail account associated with the phone before it was reset. Short of it was I decided to flash a 6.0 ROM after using the 5.1.1 ROM to get my Project Fi account activated correctly.

After flashing 6.0 and I began going through the setup wizard where I was eventually prompted to enter the credentials for the account that I had used previously. I entered my credentials and was then sent to another screen asking me to reset my Gmail password (Turns out google decided my login attempt was suspicious...). So i reluctantly reset the password not knowing I had just screwed myself(for 72 hours at least). There is a 72 hour reset time from the time you changed your account password until you're able to use it to authenticate during the setup process and until you authenticate you cant use the phone.

Not having a backup phone I took to google and found that the only way around this problem involved a USB OTG storage device loaded with an apk that causes the settings app to launch allowing you to do a real factory reset(complete wipe of all credentials and data). Resetting the phone this way removes any account associations allowing you to setup the phone as if it were new once you've re-flashed it.

Not having the tools needed to do it that way I thought about it and decided to try a few things out and eventually found my solution.

Disclaimer: I am not responsible for any damage or loss of data that may result from the following procedure.

Solution

Requirements

A computer with adb installed

USB cable

Rom with Persistent ADB Enabled (I used the 5.1.1 Stock, Rooted Project Fi ROM)

Phone booted and at the Setup Wizard

Procedure

Have the phone turned on and sitting at the startup wizard

Connect the USB to you computer and then plugin your phone ( I assume you've already setup ADB)

The phone may then prompt you and ask to verify the device fingerprint which you will say yes to

open a terminal and type:

adb shell

am start -S com.android.settings -c android.intent.category.LAUNCHER 1

This will launch the Settings.apk

***NOTE: This will completely wipe your phone!*** (Edit: The Reset program claims to wipe all internal storage but for whatever reason my SDcard data was not touched. Would still recommend pulling any wanted data from the device prior to resetting)

Go to the Backup & Reset menu and perform a factory reset

After the phone finishes resetting, proceed to boot back into Recovery mode and re-flash your ROM

The Setup Wizard will now go through the steps without the FRP authentication steps.

Again, I have only tested this on my T-Mobile Nexus 6 (using Project Fi) running 5.1.1 so your mileage may vary depending on your setup. If you find this worked or didn't work for your particular setup/situation then post your results here.

Hope this helps!

EDIT: The original solution using the USB OTG storage can be found here.

Just to clarify a bit. The problem that these two methods try and fix stems from a new feature introduced in Lollipop called FRP(Factory Reset Protection). It is meant to keep someone that has stolen a phone from being able to use it by simply doing a factory reset and reinstalling the OS. To counter this, google requires the user to verify they're the owner of the device that was reset by giving the credentials of the google account associated with the phone before it was reset. The issue arises when the password to this account is changed after the device was reset but before verifying ownership of the device during the setup process. When this happens, you have to wait 72 hours before you will be able to verify ownership using the new password.

Edit 2: Specified having a ROM with Persistent ADB Enabled as a requirement for this to work.