Merge pull request #1369 from josdotso/go-modules-docs

Documentation/dev-dependencies.md: Update for Go modules

Documentation/dev-dependencies.md

 # Managing dependencies
 
-Dex uses [glide][glide] and [glide-vc][glide-vc] to manage its [`vendor` directory][go-vendor]. A recent version of these are preferred but dex doesn't require any bleeding edge features. Either install these tools using `go get` or take an opportunity to update to a more recent version.
+## Go modules
+
+Dex uses [Go modules][go-modules] to manage its [`vendor` directory][go-vendor]. Go 1.11 or higher is recommended. While Go 1.12 is expected to finalize the Go modules feature, with Go 1.11 you should [activate the Go modules feature][go-modules-activate] before interacting with Go modules.
+
+Here is one way to activate the Go modules feature with Go 1.11.
 
 ```
-go get -u github.com/Masterminds/glide
-go get -u github.com/sgotti/glide-vc
+export GO111MODULE=on  # manually active module mode
 ```
 
-To add a new dependency to dex or update an existing one:
+You should become familiar with [module-aware `go get`][module-aware-go-get] as it can be used to add version-pinned dependencies out of band of the typical `go mod tidy -v` workflow.
 
-* Make changes to dex's source code importing the new dependency.
-* Edit `glide.yaml` to include the new dependency at a given commit SHA or change a SHA.
-* Add all transitive dependencies of the package to prevent unpinned packages.
+## Adding dependencies
 
-Tests will fail if transitive dependencies aren't included. 
+To add a new dependency to dex or update an existing one:
 
-Once `glide.yaml` describes the desired state use `make` to update `glide.lock` and `vendor`. This calls both `glide` and `glide-vc` with the set of flags that dex requires.
+1. Make changes to dex's source code importing the new dependency.
+2. You have at least three options as to how to update `go.mod` to reflect the new dependency:
+  * Run `go mod tidy -v`. This is a good option if you do not wish to immediately pin to a specific Semantic Version or commit.
+  * Run, for example, `go get <package-name>@<commit-hash>`. This is a good option when you want to immediately pin to a specific Semantic Version or commit.
+  * Manually update `go.mod`.  If one of the two options above doesn't suit you, do this -- but very carefully.
+3. Create a git commit to reflect your code (not vendor) changes. See below for tips on composing commits.
+4. Once `go.mod` describes the desired state and you've create a commit for that change, run `make revendor` to update `go.mod`, `go.sum` and `vendor`. This calls `go mod tidy -v`, `go mod vendor -v` and `go mod verify`.
+5. Create a git commit to reflect the changes made by `make revendor`. Again, see below for tips on composing commits.
 
-```
-make revendor
-```
+## Composing commits
 
 When composing commits make sure that updates to `vendor` are in a separate commit from the main changes. GitHub's UI makes commits with a large number of changes unreviewable.
 
@@ -30,6 +36,7 @@ connector/ldap: add a LDAP connector
 vendor: revendor
 ```
 
-[glide]: https://github.com/Masterminds/glide
-[glide-vc]: https://github.com/sgotti/glide-vc
+[go-modules]: https://github.com/golang/go/wiki/Modules
+[go-modules-activate]: https://github.com/golang/go/wiki/Modules#how-to-install-and-activate-module-support
 [go-vendor]: https://golang.org/cmd/go/#hdr-Vendor_Directories
+[module-aware-go-get]: https://tip.golang.org/cmd/go/#hdr-Module_aware_go_get