credentials moved to configuration, added configuration pages

docs/technical/secrets_and_config.md

@@ -77,14 +77,14 @@ You should type your function signatures! The effort is very low and it gives `d
 
 ```python
 @dlt.source
-def google_sheets(spreadsheet_id: str, tab_names: List[str] = dlt.config.value, credentials: GcpClientCredentialsWithDefault = dlt.secrets.value, only_strings: bool = False):
+def google_sheets(spreadsheet_id: str, tab_names: List[str] = dlt.config.value, credentials: GcpServiceAccountCredentials = dlt.secrets.value, only_strings: bool = False):
   ...
 ```
 Now:
 1. you are sure that you get a list of strings as `tab_names`
 2. you will get actual google credentials (see `CredentialsConfiguration` later) and your users can pass them in many different forms.
 
-In case of `GcpClientCredentialsWithDefault`
+In case of `GcpServiceAccountCredentials`
 * you may just pass the `service_json` as string or dictionary (in code and via config providers)
 * you may pass a connection string (used in sql alchemy) (in code and via config providers)
 * or default credentials will be used
@@ -331,7 +331,7 @@ It tells you exactly which paths `dlt` looked at, via which config providers and
 
 ## Working with credentials (and other complex configuration values)
 
-`GcpClientCredentialsWithDefault` is an example of a **spec**: a Python `dataclass` that describes the configuration fields, their types and default values. It also allows to parse various native representations of the configuration. Credentials marked with `WithDefaults` mixin are also to instantiate itself from the machine/user default environment ie. googles `default()` or AWS `.aws/credentials`.
+`GcpServiceAccountCredentials` is an example of a **spec**: a Python `dataclass` that describes the configuration fields, their types and default values. It also allows to parse various native representations of the configuration. Credentials marked with `WithDefaults` mixin are also to instantiate itself from the machine/user default environment ie. googles `default()` or AWS `.aws/credentials`.
 
 As an example, let's use `ConnectionStringCredentials` which represents a database connection string.
 
@@ -421,7 +421,7 @@ In fact for each decorated function a spec is synthesized. In case of `google_sh
 @configspec
 class GoogleSheetsConfiguration:
   tab_names: List[str] = None  # manadatory
-  credentials: GcpClientCredentialsWithDefault = None # mandatory secret
+  credentials: GcpServiceAccountCredentials = None # mandatory secret
   only_strings: Optional[bool] = False
 ```
 

docs/website/docs/dlt-ecosystem/destinations/duckdb.md

@@ -84,7 +84,7 @@ p = dlt.pipeline(pipeline_name='chess', destination='duckdb', dataset_name='ches
 
 This destination accepts database connection strings in format used by [duckdb-engine](https://github.com/Mause/duckdb_engine#configuration).
 
-You can configure a DuckDB destination with [secret / config values](../../general-usage/credentials.md) (e.g. using a `secrets.toml` file)
+You can configure a DuckDB destination with [secret / config values](../../general-usage/credentials) (e.g. using a `secrets.toml` file)
 ```toml
 destination.duckdb.credentials=duckdb:///_storage/test_quack.duckdb
 ```

docs/website/docs/general-usage/credentials/config_providers.md

@@ -0,0 +1,133 @@
+---
+title: Configuration Providers
+description: Configuration dlt Providers
+keywords: [credentials, secrets.toml, secrets, config, configuration, environment
+      variables, provider]
+---
+
+# Configuration Providers
+
+
+Configuration Providers in the context of the `dlt` library
+refer to different sources from which configuration values
+and secrets can be retrieved for a data pipeline.
+These providers form a hierarchy, with each having its own
+priority in determining the values for function arguments.
+
+## The provider hierarchy
+
+If function signature has arguments that may be injected, `dlt` looks for the argument values in
+providers.
+
+### Providers
+
+1. **Environment Variables**: At the top of the hierarchy are environment variables.
+   If a value for a specific argument is found in an environment variable,
+   dlt will use it and will not proceed to search in lower-priority providers.
+
+2. **Vaults (Airflow/Google/AWS/Azure)**: These are specialized providers that come
+   after environment variables. They can provide configuration values and secrets.
+   However, they typically focus on handling sensitive information.
+
+3. **`secrets.toml` and `config.toml` Files**: These files are used for storing both
+   configuration values and secrets. `secrets.toml` is dedicated to sensitive information,
+   while `config.toml` contains non-sensitive configuration data.
+
+4. **Default Argument Values**: These are the values specified in the function's signature.
+   They have the lowest priority in the provider hierarchy.
+
+### Example
+
+```python
+@dlt.source
+def google_sheets(
+    spreadsheet_id=dlt.config.value,
+    tab_names=dlt.config.value,
+    credentials=dlt.secrets.value,
+    only_strings=False
+):
+    sheets = build('sheets', 'v4', credentials=Services.from_json(credentials))
+    tabs = []
+    for tab_name in tab_names:
+        data = sheets.get(spreadsheet_id, tab_name).execute().values()
+        tabs.append(dlt.resource(data, name=tab_name))
+    return tabs
+```
+
+In case of `google_sheets()` it will look
+for: `spreadsheet_id`, `tab_names` and `credentials`.
+
+Each provider has its own key naming convention, and dlt is able to translate between them.
+
+**The argument name is a key in the lookup**.
+
+At the top of the hierarchy are Environment Variables, then `secrets.toml` and
+`config.toml` files. Providers like Airflow/Google/AWS/Azure Vaults will be inserted **after** the Environment
+provider but **before** TOML providers.
+
+For example, if `spreadsheet_id` is found in environment variable `SPREADSHEET_ID`, `dlt` will not look in TOML files
+and below.
+
+The values passed in the code **explicitly** are the **highest** in provider hierarchy. The **default values**
+of the arguments have the **lowest** priority in the provider hierarchy.
+
+:::info
+Explicit Args **>** ENV Variables **>** Vaults: Airflow etc. **>** `secrets.toml` **>** `config.toml` **>** Default Arg Values
+:::
+
+Secrets are handled only by the providers supporting them. Some providers support only
+secrets (to reduce the number of requests done by `dlt` when searching sections).
+
+1. `secrets.toml` and environment may hold both config and secret values.
+1. `config.toml` may hold only config values, no secrets.
+1. Various vaults providers hold only secrets, `dlt` skips them when looking for values that are not
+   secrets.
+
+> Context-aware providers will activate in the right environments i.e. on Airflow or AWS/GCP VMachines.
+
+## Provider key formats
+
+### TOML vs. Environment Variables
+
+Providers may use different formats for the keys. `dlt` will translate the standard format where
+sections and key names are separated by "." into the provider-specific formats.
+
+1. For TOML, names are case-sensitive and sections are separated with ".".
+1. For Environment Variables, all names are capitalized and sections are separated with double
+   underscore "__".
+
+Example: When `dlt` evaluates the request `dlt.secrets["my_section.gcp_credentials"]` it must find
+the `private_key` for Google credentials. It will look
+
+1. first in env variable `MY_SECTION__GCP_CREDENTIALS__PRIVATE_KEY` and if not found,
+1. in `secrets.toml` with key `my_section.gcp_credentials.private_key`.
+
+### Environment provider
+
+Looks for the values in the environment variables.
+
+### TOML provider
+
+TOML provider uses two TOML files: `secrets.toml` to store secrets and `config.toml` to store
+configuration values. The default `.gitignore` file prevents secrets from being added to source
+control and pushed. The `config.toml` may be freely added.
+
+> **Toml provider always loads those files from `.dlt` folder** which is looked **relative to the
+> current Working Directory**.
+
+Example: If your working directory is `my_dlt_project` and your project has the following structure:
+
+```
+my_dlt_project:
+  |
+  pipelines/
+    |---- .dlt/secrets.toml
+    |---- google_sheets.py
+```
+
+and you run `python pipelines/google_sheets.py` then `dlt` will look for `secrets.toml` in
+`my_dlt_project/.dlt/secrets.toml` and ignore the existing
+`my_dlt_project/pipelines/.dlt/secrets.toml`.
+
+If you change your working directory to `pipelines` and run `python google_sheets.py` it will look for
+`my_dlt_project/pipelines/.dlt/secrets.toml` as (probably) expected.