oc login: Implement --context flag

The flag can be used to tell oc what context name to use when updating
kubeconfig. If a matching context already exists, it is replaced
altogether, including the linked cluster and authInfo. This means that
the configured cluster and authInfo names are also reused.

Author: tchap

pkg/cli/login/login.go

@@ -44,6 +44,9 @@ var (
 		# Log in to the given server with the given credentials (will not prompt interactively)
 		oc login localhost:8443 --username=myuser --password=mypass
 
+		# Log in to the given server as myuser and use a custom kubeconfig context name. 
+		oc login localhost:8443 --username=myuser --context=local
+
 		# Log in to the given server through a browser
 		oc login localhost:8443 --web --callback-port 8280
 
@@ -162,6 +165,7 @@ func (o *LoginOptions) Complete(f kcmdutil.Factory, cmd *cobra.Command, args []s
 	o.Token = kcmdutil.GetFlagString(cmd, "token")
 
 	o.DefaultNamespace, _, _ = f.ToRawKubeConfigLoader().Namespace()
+	o.Context = kcmdutil.GetFlagString(cmd, "context")
 
 	o.PathOptions = kclientcmd.NewDefaultPathOptions()
 	// we need to set explicit path if one was specified, since NewDefaultPathOptions doesn't do it for us

pkg/cli/login/loginoptions.go

@@ -75,6 +75,7 @@ type LoginOptions struct {
 	StartingKubeConfig *kclientcmdapi.Config
 	DefaultNamespace   string
 	Config             *restclient.Config
+	Context            string
 
 	// cert data to be used when authenticating
 	CertFile string
@@ -570,7 +571,7 @@ func (o *LoginOptions) SaveConfig() (bool, error) {
 		return false, err
 	}
 
-	configToWrite, err := cliconfig.MergeConfig(*o.StartingKubeConfig, *newConfig)
+	configToWrite, err := o.mergeConfig(*newConfig)
 	if err != nil {
 		return false, err
 	}
@@ -593,6 +594,44 @@ func (o *LoginOptions) SaveConfig() (bool, error) {
 	return created, nil
 }
 
+func (o *LoginOptions) mergeConfig(additionalConfig kclientcmdapi.Config) (*kclientcmdapi.Config, error) {
+	if o.Context == "" {
+		return cliconfig.MergeConfig(*o.StartingKubeConfig, additionalConfig)
+	}
+
+	// Unwrap additionalConfig. There is expected to be just a single context, cluster and authInfo.
+	var (
+		newContext  kclientcmdapi.Context
+		newCluster  kclientcmdapi.Cluster
+		newAuthInfo kclientcmdapi.AuthInfo
+	)
+	for _, v := range additionalConfig.Contexts {
+		newContext = *v
+	}
+	for _, v := range additionalConfig.Clusters {
+		newCluster = *v
+	}
+	for _, v := range additionalConfig.AuthInfos {
+		newAuthInfo = *v
+	}
+
+	ret := *o.StartingKubeConfig
+
+	// If the selected context exists, replace the linked cluster and authInfo.
+	// When there is no match, we use the new objects, but o.Context is still used as the new context name.
+	existingContext, ok := ret.Contexts[o.Context]
+	if ok {
+		newContext.Cluster = existingContext.Cluster
+		newContext.AuthInfo = existingContext.AuthInfo
+	}
+
+	ret.Clusters[newContext.Cluster] = &newCluster
+	ret.AuthInfos[newContext.AuthInfo] = &newAuthInfo
+	ret.Contexts[o.Context] = &newContext
+	ret.CurrentContext = o.Context
+	return &ret, nil
+}
+
 func (o *LoginOptions) whoAmI(clientConfig *restclient.Config) (*userv1.User, error) {
 	if o.whoAmIFunc != nil {
 		return o.whoAmIFunc(clientConfig)