upload/koji: add support for GSSAPI/Kerberos auth

Prior this commit we only had support for username/password authentication
in the koji integration. This wasn't particularly useful because this
auth type isn't used in any production instance.

This commit adds the support for GSSAPI/Kerberos authentication.
The implementation uses kerby library which is very lightweight wrapper
around C gssapi library.

Also, the koji unit test and the run-koji-container script were modified
so the GSSAPI auth is fully tested.

.github/koji.conf

@@ -66,3 +66,5 @@ plugins = runroot
 
 ; use the fast upload feature of koji by default
 use_fast_upload = yes
+
+serverca = /tmp/osbuild-composer-koji-test/ca-crt.pem

.github/krb5.conf

@@ -0,0 +1,7 @@
+include /etc/krb5.conf
+
+[realms]
+    LOCAL = {
+        kdc = localhost
+        admin_server = localhost
+    }

.github/workflows/tests.yml

@@ -40,6 +40,10 @@ jobs:
       - name: Install golangci-lint
         run: curl -sfL https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh| sh -s -- -b $(go env GOPATH)/bin v1.30.0
 
+        # This is needed to lint internal/upload/koji package
+      - name: Install kerberos devel package
+        run: sudo apt-get install -y libkrb5-dev
+
       - name: Run golangci-lint
         run: $(go env GOPATH)/bin/golangci-lint run --timeout 5m0s
 
@@ -73,7 +77,7 @@ jobs:
         # and installed here. See the last line of the script.
       - name: Install koji client
         run: |
-          sudo apt-get install -y libkrb5-dev
+          sudo apt-get install -y libkrb5-dev krb5-config
           python -m pip install --upgrade pip
           pip install koji
           sudo cp .github/koji.conf /etc/koji.conf
@@ -81,7 +85,7 @@ jobs:
       - name: Run unit tests
         run: |
           sudo internal/upload/koji/run-koji-container.sh start
-          go test -v -race -covermode atomic -coverprofile=coverage.txt -tags koji_test ./internal/upload/koji
+          env KRB5_CONFIG=../../../.github/krb5.conf go test -v -race -covermode atomic -coverprofile=coverage.txt -tags koji_test ./internal/upload/koji
           sudo internal/upload/koji/run-koji-container.sh stop
 
       - name: Send coverage to codecov.io