Add ability to specify github enpoints for creds

The GitHub credentials section now allows setting some API endpoints
that point the github client and the runner setup script to the propper
URLs. This allows us to use garm with an on-prem github enterprise server.

Signed-off-by: Gabriel Adrian Samfira <gsamfira@cloudbasesolutions.com>

config/config.go

@@ -18,7 +18,6 @@ import (
 	"crypto/tls"
 	"crypto/x509"
 	"fmt"
-	"io/ioutil"
 	"log"
 	"net"
 	"os"
@@ -66,7 +65,13 @@ const (
 	// of time and no new updates have been made to it's state, it will be removed.
 	DefaultRunnerBootstrapTimeout = 20
 
+	// DefaultGithubURL is the default URL where Github or Github Enterprise can be accessed
 	GithubBaseURL = "https://github.com"
+
+	// defaultBaseURL is the default URL for the github API
+	defaultBaseURL = "https://api.github.com/"
+	// uploadBaseURL is the default URL for guthub uploads
+	uploadBaseURL = "https://uploads.github.com/"
 )
 
 var (
@@ -190,15 +195,69 @@ func (d *Default) Validate() error {
 // Github hold configuration options specific to interacting with github.
 // Currently that is just a OAuth2 personal token.
 type Github struct {
-	Name        string `toml:"name" json:"name"`
-	Description string `toml:"description" json:"description"`
-	OAuth2Token string `toml:"oauth2_token" json:"oauth2-token"`
+	Name          string `toml:"name" json:"name"`
+	Description   string `toml:"description" json:"description"`
+	OAuth2Token   string `toml:"oauth2_token" json:"oauth2-token"`
+	APIBaseURL    string `toml:"api_base_url" json:"api-base-url"`
+	UploadBaseURL string `toml:"upload_base_url" json:"upload-base-url"`
+	BaseURL       string `toml:"base_url" json:"base-url"`
+	// CACertBundlePath is the path on disk to a CA certificate bundle that
+	// can validate the endpoints defined above. Leave empty if not using a
+	// self signed certificate.
+	CACertBundlePath string `toml:"ca_cert_bundle" json:"ca-cert-bundle"`
+}
+
+func (g *Github) APIEndpoint() string {
+	if g.APIBaseURL != "" {
+		return g.APIBaseURL
+	}
+	return defaultBaseURL
+}
+
+func (g *Github) CACertBundle() ([]byte, error) {
+	if g.CACertBundlePath == "" {
+		// No CA bundle defined.
+		return nil, nil
+	}
+	if _, err := os.Stat(g.CACertBundlePath); err != nil {
+		return nil, errors.Wrap(err, "accessing CA bundle")
+	}
+
+	contents, err := os.ReadFile(g.CACertBundlePath)
+	if err != nil {
+		return nil, errors.Wrap(err, "reading CA bundle")
+	}
+
+	roots := x509.NewCertPool()
+	if ok := roots.AppendCertsFromPEM(contents); !ok {
+		return nil, fmt.Errorf("failed to parse CA cert bundle")
+	}
+
+	return contents, nil
+}
+
+func (g *Github) UploadEndpoint() string {
+	if g.UploadBaseURL == "" {
+		if g.APIBaseURL != "" {
+			return g.APIBaseURL
+		}
+		return uploadBaseURL
+	}
+	return g.UploadBaseURL
+}
+
+func (g *Github) BaseEndpoint() string {
+	if g.BaseURL != "" {
+		return g.BaseURL
+	}
+	return GithubBaseURL
 }
 
 func (g *Github) Validate() error {
 	if g.OAuth2Token == "" {
 		return fmt.Errorf("missing github oauth2 token")
 	}
+
 	return nil
 }
 
@@ -372,7 +431,7 @@ func (t *TLSConfig) TLSConfig() (*tls.Config, error) {
 
 	var roots *x509.CertPool
 	if t.CACert != "" {
-		caCertPEM, err := ioutil.ReadFile(t.CACert)
+		caCertPEM, err := os.ReadFile(t.CACert)
 		if err != nil {
 			return nil, err
 		}