API: fixes return codes, documentation updated with status codes, tests added

The users API updated with return codes, e.g. if required parameters are missing
a `400 Bad Request` error is returned instead of `404`. Fixes return codes of functions,
e.g. deletion of a ssh key is an idempotent function now.
The API documentation is updated to reflect the current status of the API. Descriptions
are more detailed and complete, infos to return values are added to all functions.

1 files changed, 92 insertions, 26 deletions

diff --git a/doc/api/users.md b/doc/api/users.md
index e5893638fdc..96aebffafd8 100644
--- a/doc/api/users.md
+++ b/doc/api/users.md
@@ -88,36 +88,47 @@ Return values:
 
 
 ## User creation
-Create user. Available only for admin
+
+Creates a new user. Note only administrators can create new users.
 
 ```
 POST /users
 ```
 
 Parameters:
-+ `email` (required)                  - Email
-+ `password` (required)               - Password
-+ `username` (required)               - Username
-+ `name` (required)                   - Name
-+ `skype`                             - Skype ID
-+ `linkedin`                          - Linkedin
-+ `twitter`                           - Twitter account
-+ `projects_limit`                    - Number of projects user can create
-+ `extern_uid`                        - External UID
-+ `provider`                          - External provider name
-+ `bio`                               - User's bio
 
-Will return created user with status `201 Created` on success, or `404 Not
-found` on fail.
++ `email` (required)          - Email
++ `password` (required)       - Password
++ `username` (required)       - Username
++ `name` (required)           - Name
++ `skype` (optional)          - Skype ID
++ `linkedin` (optional)       - Linkedin
++ `twitter` (optional)        - Twitter account
++ `projects_limit` (optional) - Number of projects user can create
++ `extern_uid` (optional)     - External UID
++ `provider` (optional)       - External provider name
++ `bio` (optional)            - User's bio
+
+Return values:
+
++ `201 Created` on success and returns the new user
++ `400 Bad Request` if one of the required attributes is missing from the request
++ `401 Unauthorized` if the user is not authorized
++ `403 Forbidden` if the user is not allowed to create a new user (must be admin)
++ `404 Not Found` if something else fails
++ `409 Conflict` if a user with the same email address or username already exists
+
 
 ## User modification
-Modify user. Available only for admin
+
+Modifies an existing user. Only administrators can change attributes of a user.
 
 ```
 PUT /users/:id
 ```
 
 Parameters:
+
 + `email`                             - Email
 + `username`                          - Username
 + `name`                              - Name
@@ -130,23 +141,42 @@ Parameters:
 + `provider`                          - External provider name
 + `bio`                               - User's bio
 
+Return values:
+
++ `200 Ok` on success and returns the new user
++ `401 Unauthorized` if the user is not authorized
++ `403 Forbidden` if the user is not allowed to create a new user (must be admin)
++ `404 Not Found` if something else fails
+
+Note, at the moment this method does only return a 404 error, even in cases where a 409 (Conflict) would
+be more appropriate, e.g. when renaming the email address to some exsisting one.
 
-Will return created user with status `200 OK` on success, or `404 Not
-found` on fail.
 
 ## User deletion
-Delete user. Available only for admin
+
+Deletes a user. Available only for administrators. This is an idempotent function, calling this function
+for a non-existent user id still returns a status code `200 Ok`. The JSON response differs if the user
+was actually deleted or not. In the former the user is returned and in the latter not.
 
 ```
 DELETE /users/:id
 ```
 
-Will return deleted user with status `200 OK` on success, or `404 Not
-found` on fail.
+Parameters:
+
++ `id` (required) - The ID of the user
+
+Return values:
+
++ `200 Ok` on success and returns the deleted user
++ `401 Unauthorized` if the user is not authorized
++ `403 Forbidden` if the user is not allowed to create a new user (must be admin)
++ `404 Not Found` if user with ID not found or something else fails
+
 
 ## Current user
 
-Get currently authenticated user.
+Gets currently authenticated user.
 
 ```
 GET /user
@@ -169,6 +199,13 @@ GET /user
 }
 ```
 
+Return values:
+
++ `200 Ok` on success and returns the current user
++ `401 Unauthorized` if the user is not authorized
++ `404 Not Found` if something else fails
+
+
 ## List SSH keys
 
 Get a list of currently authenticated user's SSH keys.
@@ -196,6 +233,17 @@ GET /user/keys
 ]
 ```
 
+Parameters:
+
++ **none**
+
+Return values:
+
++ `200 Ok` on success and a list of ssh keys
++ `401 Unauthorized` if the user is not authenticated
++ `404 Not Found` if something else fails
+
+
 ## Single SSH key
 
 Get a single key.
@@ -217,9 +265,17 @@ Parameters:
       soW6NUlfDzpvZK2H5E7eQaSeP3SAwGmQKUFHCddNaP0L+hM7zhFNzjFvpaMgJw0="
 }
 ```
+
+Return values:
+
++ `200 Ok` on success and the ssh key with ID
++ `401 Unauthorized` if it is not allowed to access the user
++ `404 Not Found` if the ssh key with ID not found
+
+
 ## Add SSH key
 
-Create new key owned by currently authenticated user
+Creates a new key owned by the currently authenticated user.
 
 ```
 POST /user/keys
@@ -230,12 +286,18 @@ Parameters:
 + `title` (required) - new SSH Key's title
 + `key` (required) - new SSH key
 
-Will return created key with status `201 Created` on success, or `404 Not
-found` on fail.
+Return values:
+
++ `201 Created` on success and the added key
++ `400 Bad Request` if one of the required attributes is not given
++ `401 Unauthorized` if user is not authorized to add ssh key
++ `404 Not Found` if something else fails
+
 
 ## Delete SSH key
 
-Delete key owned by currently authenticated user
+Deletes key owned by currently authenticated user. This is an idempotent function and calling it on a key that is already
+deleted or not available results in `200 Ok`.
 
 ```
 DELETE /user/keys/:id
@@ -245,4 +307,8 @@ Parameters:
 
 + `id` (required) - SSH key ID
 
-Will return `200 OK` on success, or `404 Not Found` on fail.
+Return values:
+
++ `200 Ok` on success
++ `401 Unauthorized` if user is not allowed to delete they key
++ `404 Not Found` if something else fails