GraphQL API token authentication not working on Self-Managed instance with relative URL

Summary

Access token bearer authorization appears to be broken when running GitLab from a relative URL.

Steps to reproduce

Install GitLab with a relative URL (e.g. EXTERNAL_URL="http://dev.local/gitlab"), we followed the instructions at https://about.gitlab.com/install/#ubuntu
Create access token with all scopes
Attempt to query current user via GraphQL

What is the current bug behavior?

null returned for current user.

What is the expected correct behavior?

The current user name should be returned.

Relevant logs and/or screenshots

% curl -k 'https://dev.local/gitlab/api/graphql' --header "Authorization: Bearer $GRAPHQL_TOKEN_REL" --header "Content-Type: application/json" --request POST --data "{\"query\": \"query {currentUser {name}}\"}"
{"data":{"currentUser":null}}%

% curl -k 'https://gitlab.dev.local/api/graphql' --header "Authorization: Bearer $GRAPHQL_TOKEN_SUB" --header "Content-Type: application/json" --request POST --data "{\"query\": \"query {currentUser {name}}\"}"
{"data":{"currentUser":{"name":"Ian Hattendorf"}}}%

Results of GitLab environment info

Expand for output related to GitLab environment info

$ sudo gitlab-rake gitlab:env:info

System information
System:		Ubuntu 20.04
Current User:	git
Using RVM:	no
Ruby Version:	2.6.6p146
Gem Version:	2.7.10
Bundler Version:1.17.3
Rake Version:	12.3.3
Redis Version:	5.0.9
Git Version:	2.28.0
Sidekiq Version:5.2.9
Go Version:	unknown
GitLab information
Version:	13.3.5
Revision:	467cb4161ad
Directory:	/opt/gitlab/embedded/service/gitlab-rails
DB Adapter:	PostgreSQL
DB Version:	11.7
URL:		https://dev.local/gitlab
HTTP Clone URL:	https://dev.local/gitlab/some-group/some-project.git
SSH Clone URL:	git@dev.local:some-group/some-project.git
Using LDAP:	no
Using Omniauth:	yes
Omniauth Providers:
GitLab Shell
Version:	13.6.0
Repository storage paths:
- default: 	/var/opt/gitlab/git-data/repositories
GitLab Shell path:		/opt/gitlab/embedded/service/gitlab-shell
Git:		/opt/gitlab/embedded/bin/git

Results of GitLab application Check

Expand for output related to the GitLab application check

$ sudo gitlab-rake gitlab:check SANITIZE=true
Checking GitLab subtasks ...
Checking GitLab Shell ...
GitLab Shell: ... GitLab Shell version >= 13.6.0 ? ... OK (13.6.0)
Running /opt/gitlab/embedded/service/gitlab-shell/bin/check
Internal API available: OK
Redis available via internal API: OK
gitlab-shell self-check successful
Checking GitLab Shell ... Finished
Checking Gitaly ...
Gitaly: ... default ... OK
Checking Gitaly ... Finished
Checking Sidekiq ...
Sidekiq: ... Running? ... yes
Number of Sidekiq processes ... 1
Checking Sidekiq ... Finished
Checking Incoming Email ...
Incoming Email: ... Reply by email is disabled in config/gitlab.yml
Checking Incoming Email ... Finished
Checking LDAP ...
LDAP: ... LDAP is disabled in config/gitlab.yml
Checking LDAP ... Finished
Checking GitLab App ...
Git configured correctly? ... yes
Database config exists? ... yes
All migrations up? ... yes
Database contains orphaned GroupMembers? ... no
GitLab config exists? ... yes
GitLab config up to date? ... yes
Log directory writable? ... yes
Tmp directory writable? ... yes
Uploads directory exists? ... yes
Uploads directory has correct permissions? ... yes
Uploads directory tmp has correct permissions? ... skipped (no tmp uploads folder yet)
Init script exists? ... skipped (omnibus-gitlab has no init script)
Init script up-to-date? ... skipped (omnibus-gitlab has no init script)
Projects have namespace: ...
5/1 ... yes
5/2 ... yes
Redis version >= 4.0.0? ... yes
Ruby version >= 2.5.3 ? ... yes (2.6.6)
Git version >= 2.24.0 ? ... yes (2.28.0)
Git user has default SSH configuration? ... yes
Active users: ... 3
Is authorized keys file accessible? ... yes
GitLab configured to store new projects in hashed storage? ... yes
All projects are in hashed storage? ... yes
Checking GitLab App ... Finished
Checking GitLab subtasks ... Finished