"Unable to login" error during the authentication on VAMI in VCSA 6.7

Products

VMware vCenter Server

Issue/Introduction

Symptoms:

Root authentication works on SSH, logging into VMware Appliance management (VAMI) using the root account and its password fails on Appliance Management page (port 5480) of VCSA 6.7.x.
You see the error:

Unable to Login

This error is observed only in VCSA 6.7.
In the applmgmt log file at /var/log/vmware/applmgmt/applmgmt.log , you see entries similar to:

File /usr/lib/vmware-vapi/lib/python/vapi_runtime-2.100.0-py2.py3-none-any.whl/vmware/vapi/security/user_password.py", line 89, in _get_username_password_from_auth_header username, password = user_password_str.split(':')
ValueError: too many values to unpack (expected 2)
2018-08-24T19:25:30.716 [2399]INFO:twisted:"127.0.0.1" - - [24/Aug/2018:19:25:29 +0000] "POST /rest/com/vmware/cis/session HTTP/1.0" 500 187 "https://x.x.x.x:5480/login" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/68.0.3440.106 Safari/537.36"

Note: The preceding log excerpts are only examples. Date, time, and environmental variables may vary depending on your environment.

Environment

VMware vCenter Server Appliance 6.7.x

Resolution

To resolve the issue follow the steps below:

Ensure Appliance Management service is up and running before proceeding.
Confirm the "applmgmt" service is running by running the following command through SSH session to vCenter.

service-control --status --all
Stopped:
vmcam vmware-imagebuilder vmware-mbcs vmware-netdumper vmware-rbd-watchdog vmware-vcha vsan-dps
Running:
applmgmt lwsmd pschealth vmafdd vmcad vmdird vmdnsd vmonapi vmware-analytics vmware-certificatemanagement vmware-cis-license vmware-cm vmware-content-library vmware-eam vmware-perfcharts vmware-pod vmware-postgres-archiver vmware-rhttpproxy vmware-sca vmware-sps vmware-statsmonitor vmware-sts-idmd vmware-stsd vmware-topologysvc vmware-updatemgr vmware-vapi-endpoint vmware-vmon vmware-vpostgres vmware-vpxd vmware-vpxd-svcs vmware-vsan-health vmware-vsm vsphere-client vsphere-ui

If the "applmgmt" is stopped, start it using : service-control --start applmgmt
If issue still exist after starting "applmgmt" service, change the root password on the VCSA 6.7.x.

Process to change the root password on the VCSA 6.7.x.:

To resolve this issue, change the root password on the VCSA 6.7.x.

You many need to Log in to the Direct Console User Interface of the vCenter Server Appliance to enable SSH session, refer: Enable Access to the Appliance Bash Shell
To change the root password use passwd command from an SSH session.
If SSH is not accessible using root credentials, refer: How to reset the lost or forgotten root password in vCenter Server Appliance 6.5 & 6.7 OR How to reset the lost or forgotten root password in vCenter Server Appliance 6.7 U1 and later

Note: Do not include special character colon ":" in the password. The exclamation mark "!" may give you problems as well.

After changing the root password log into VCSA-VAMI, restart of the service not required, it takes effect immediately.