How to fix the 'too many redirects' error in Magento 2

 This article presents a technique to the redirect loop error while logging in to the Magento admin panel.

Did installation an existing Magento keep.

Went to the Magento admin login web page

Entered admin username and password

Got the ERR_TOO_MANY_REDIRECTS mistakes

The website has a redirect loop
ERR_TOO_MANY_REDIRECTS

Cause

The problem is with the Cookie Domain for the Magento website.

i.e. the Magento configuration setting for web/cookie/cookie_domain

My Magento website domain was magento.test.
But, in the configuration settings, it was set as magento.host.

Solution

We need to update the configuration settings value for path web/cookie/cookie_domain with the correct cookie-domain name.

There are two ways to update the configuration settings values.

1) Update the configuration setting from the command line

Show the config value:

bin/magento config:show web/cookie/cookie_domain

Set the config value:

bin/magento config:set web/cookie/cookie_domain magento.test

2) Update database table rows

This one seems better as we can see the value for different stores/websites.

Check the values in the database table:

> SELECT * FROM core_config_data WHERE path LIKE '%web/cookie/cookie_domain%';
+-----------+---------+----------+--------------------------+------------------+---------------------+
| config_id | scope   | scope_id | path                     | value            | updated_at          |
+-----------+---------+----------+--------------------------+------------------+---------------------+
|        18 | default |        0 | web/cookie/cookie_domain | magento.host     | 2020-08-26 15:24:07 |
|      1033 | stores  |        3 | web/cookie/cookie_domain | ca.magento.test  | 2020-06-16 16:57:47 |
+-----------+---------+----------+--------------------------+------------------+---------------------+

Update the config setting value:

> UPDATE core_config_data SET value = 'magento.test' WHERE config_id = 18;

Clear Cache

bin/magento cache:flush

Now, you should be able to login to the Magento admin.